Begin yet another model refactor

Use native ListModel which require a lot of changes, but should be
much faster than the old way which exponentially slowed down to a crawl.
Also fix some popup bugs (leave/forget).

Not working yet: side pane keyboard controls, proper highlight,
room & member filtering, local echo replacement

.gitmodules

@@ -7,3 +7,6 @@
 [submodule "submodules/hsluv-c"]
 	path = submodules/hsluv-c
 	url = https://github.com/hsluv/hsluv-c
+[submodule "submodules/gel"]
+	path = submodules/gel
+	url = https://github.com/Cutehacks/gel