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/Client.ts

@@ -0,0 +1,35 @@
+class ClientClass {
+  async post(url: string, data?: Record<string, any>): Promise<any> {
+    const res = await fetch(url, {
+      method: 'POST',
+      headers: {
+        accept: 'application/json',
+        'content-type': 'application/json'
+      },
+      body: data !== undefined ? JSON.stringify(data) : undefined
+    })
+    let msg
+    try {
+      msg = await res.json()
+    } catch (e) {
+      throw new SimpleError(res.status, `🛑 ${res.status} ${res.statusText}`)
+    }
+    if ('error' in msg) throw new SimpleError(msg.error.code, msg.error.message)
+    return msg
+  }
+}
+
+export const Client = new ClientClass()
+export interface ISimpleError extends Error {
+  code: number
+}
+
+class SimpleError extends Error implements ISimpleError {
+  code: number
+  constructor(code: number, message: string) {
+    super(message)
+    this.code = code
+  }
+}
+
+export default Client