More efficient flat file list format and various UX improvements (#3)

This is a major upgrade with assorted things included.

- Navigation flows improved, search appears in URL history, cleared when navigating to another folder
- More efficient file list format for faster loads
- Efficient updates, never re-send full root another time (except at connection)
- Large number of watching and filelist updates (inotify issues remain)
- File size coloring
- Fixed ZIP generation random glitches (thread race condition)
- Code refactoring, cleanup, typing fixes
- More tests

Reviewed-on: #3

frontend/src/repositories/Document.ts

@@ -0,0 +1,42 @@
+export type FUID = string
+
+export type Document = {
+  loc: string
+  name: string
+  key: FUID
+  size: number
+  sizedisp: string
+  mtime: number
+  modified: string
+  haystack: string
+  dir: boolean
+}
+
+export type errorEvent = {
+  error: {
+    code: number
+    message: string
+    redirect: string
+  }
+}
+
+// Raw types the backend /api/watch sends us
+
+export type FileEntry = [
+  number,  // level
+  string,  // name
+  FUID,
+  number, //mtime
+  number, // size
+  number, // isfile
+]
+
+export type UpdateEntry = ['k', number] | ['d', number] | ['i', Array<FileEntry>]
+
+// Helper structure for selections
+export interface SelectedItems {
+  keys: FUID[]
+  docs: Record<FUID, Document>
+  recursive: Array<[string, string, Document]>
+  missing: Set<FUID>
+}