Add file watcher to re-generate thumbnails

Previously files added while the server is running would not have
thumbnails until after the server was restarted. Now we watch the
BASE_PATH for added/renamed files in order to re-gen the thumbnail.

Cargo.lock

@@ -816,6 +816,18 @@ version = "0.1.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e88a8acf291dafb59c2d96e8f59828f3838bb1a70398823ade51a84de6a6deed"
 
+[[package]]
+name = "filetime"
+version = "0.2.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3ed85775dcc68644b5c950ac06a2b23768d3bc9390464151aaf27136998dcf9e"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "redox_syscall",
+ "winapi 0.3.9",
+]
+
 [[package]]
 name = "flate2"
 version = "1.0.17"
@@ -834,6 +846,25 @@ version = "1.0.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3f9eec918d3f24069decb9af1554cad7c880e2da24a9afd88aca000531ab82c1"
 
+[[package]]
+name = "fsevent"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5ab7d1bd1bd33cc98b0889831b72da23c0aa4df9cec7e0702f46ecea04b35db6"
+dependencies = [
+ "bitflags",
+ "fsevent-sys",
+]
+
+[[package]]
+name = "fsevent-sys"
+version = "2.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f41b048a94555da0f42f1d632e2e19510084fb8e303b0daa2816e733fb3644a0"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "fuchsia-zircon"
 version = "0.3.3"
@@ -1126,10 +1157,12 @@ dependencies = [
  "hmac",
  "image",
  "jsonwebtoken",
+ "notify",
  "rayon",
  "serde",
  "serde_json",
  "sha2",
+ "tokio",
  "walkdir",
 ]
 
@@ -1143,6 +1176,26 @@ dependencies = [
  "hashbrown",
 ]
 
+[[package]]
+name = "inotify"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4816c66d2c8ae673df83366c18341538f234a26d65a9ecea5c348b453ac1d02f"
+dependencies = [
+ "bitflags",
+ "inotify-sys",
+ "libc",
+]
+
+[[package]]
+name = "inotify-sys"
+version = "0.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e74a1aa87c59aeff6ef2cc2fa62d41bc43f54952f55652656b18a02fd5e356c0"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "instant"
 version = "0.1.6"
@@ -1231,6 +1284,12 @@ version = "1.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
 
+[[package]]
+name = "lazycell"
+version = "1.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "830d08ce1d1d941e6b30645f1a0eb5643013d835ce3779a5fc208261dbe10f55"
+
 [[package]]
 name = "libc"
 version = "0.2.77"
@@ -1372,6 +1431,18 @@ dependencies = [
  "winapi 0.2.8",
 ]
 
+[[package]]
+name = "mio-extras"
+version = "2.0.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "52403fe290012ce777c4626790c8951324a2b9e3316b3143779c72b029742f19"
+dependencies = [
+ "lazycell",
+ "log",
+ "mio",
+ "slab",
+]
+
 [[package]]
 name = "mio-uds"
 version = "0.6.8"
@@ -1416,6 +1487,24 @@ dependencies = [
  "version_check 0.1.5",
 ]
 
+[[package]]
+name = "notify"
+version = "4.0.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "80ae4a7688d1fab81c5bf19c64fc8db920be8d519ce6336ed4e7efe024724dbd"
+dependencies = [
+ "bitflags",
+ "filetime",
+ "fsevent",
+ "fsevent-sys",
+ "inotify",
+ "libc",
+ "mio",
+ "mio-extras",
+ "walkdir",
+ "winapi 0.3.9",
+]
+
 [[package]]
 name = "num-bigint"
 version = "0.2.6"