* Plugin callsigns, filechangehandler thread bug fix, plugin file perms

- Plugins are now assigned a callsign (a random string), which they use for all internal identification, like resource fetching and method calls. This is to ensure that plugins only access their own resources and methods.
- Made FileChangeHandler send off events to a queue, that is then consumed by the Loader, instead of calling import_plugin on its own, since that caused weird issues with the event loop and the thread watchdog is using.
- Plugins are now owned by root and have read-only permissions. This is handled automatically.

* Improved general look and feel of plugin tab

* Make all plugin entries have the same padding between them

* Make "No plugins installed" text look the same as "No new notifications"

Co-authored-by: WerWolv <werwolv98@gmail.com>

Fixed a bug where steam would sometimes fire message events on its own, causing them to be displayed as plugin titles.

- Integrated plugin downloader/installer. It accepts POST requests at /browser/install_plugin, containing an artifact (basically an author/repo string like you'd find on github), and a release version, then fetches the zip file from the repo releases and unzips it inside the plugin dir, after asking for user confirmation (pop-up message in the plugin menu).
- Injector get_tab method. Basically get_tabs with the usual search for a specific tab. Decided to implement this because it was needed again and again, and we kept pasting the same list search one-liner.
- Utilities now have access to the main PluginManager class

also fixed fetch_nocors

* Initial commit. Untested

* various fixes

Core functionality confirmed working:
 - Iframe injection into steam client
 - Plugin fetching from the iframe
 - Plugin opening

* Added function to fetch resources from steam

* Improved injector module, added server-js communication

- Injector module now has methods for better lower-level manipulation of the tab debug websocket.
- Our "front-end" can now communicate with the manager (2-way), completely bypassing the chromium sandbox. This works via a dirty debug console trick, whoever wants to know how it works can take a look at the code.
- Added utility methods file, along with an implementation of the aiohttp client that our "front-end" can access, via the system described above.
- Added js implementations of the communication system described above, which can be imported by plugins.

* Added steam_resource endpoint

* Added basic installer script

* retry logic bug fix

* fixed library injection, event propagation, websocket handling

- library is injected directly into the plugins as well as the plugin list
- resolveMethodCall is implemented in the plugin_list.js file, which in turns calls window.sendMessage on the iframe to propagate the event
- websocket method calls are processed in their own tasks now, so as not to block on long-running calls.

Co-authored-by: tza <tza@hidden>
Co-authored-by: WerWolv <werwolv98@gmail.com>