Better sending of mentions support

There are two annoyances when trying to mention someone:

1. Clicking their name on the timeline takes you to their member info, rather than inserting a mention like in the legacy apps (and the legacy apps have a "mention" menu item in the member info)
2. When you type `@...` it displays in alphabetical order(?), which can display really old unused accounts before recently active accounts (e.g `@matthew:ara.....` vs `@matthew:matrix....`)