initial browser/installer commit, injector get_tab and stateful utils

- 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

plugin_loader/utilities.py

@@ -1,18 +1,25 @@
 from aiohttp import ClientSession
 
-async def http_request(method="", url="", **kwargs):
-    async with ClientSession() as web:
-        res = await web.request(method, url, **kwargs)
-        return {
-            "status": res.status,
-            "headers": dict(res.headers),
-            "body": await res.text()
+class Utilities:
+    def __init__(self, context) -> None:
+        self.context = context
+        self.util_methods = {
+            "ping": self.ping,
+            "http_request": self.http_request,
+            "confirm_plugin_install": self.confirm_plugin_install
         }
 
-async def ping(**kwargs):
-    return "pong"
+    async def confirm_plugin_install(self, request_id):
+        return await self.context.plugin_browser.confirm_plugin_install(request_id)
 
-util_methods = {
-    "ping": ping,
-    "http_request": http_request
-}
+    async def http_request(self, method="", url="", **kwargs):
+        async with ClientSession() as web:
+            res = await web.request(method, url, **kwargs)
+            return {
+                "status": res.status,
+                "headers": dict(res.headers),
+                "body": await res.text()
+            }
+
+    async def ping(self, **kwargs):
+        return "pong"