Make username/logout button appear at every page

Used the context parameter 'user', which is included by default, to access
data from the user that is logged in without needing to check for it in
every view and add it to the context dictionary manually.

Note that the views that do check for this have not had them removed
because they might still be relevant in their own individual templates.
Changed replay button in game to a circular arrow

Changed the symbol for the replay button from an infintiy sign to a
circular arrow.
Mostly fixed the "sticky key" bug in the game

Because of a previous change to make the game over message a js alert,
users have occasionally been experiencing behavior where a key gets
"stuck" and clicking replay caused the player to move as if the button was
still pressed until it was pressed again. This was fixed by creating a
message in HTML at the bottom of the screen alongside the replay button.
This means that the "sticky key" bug does not occur unless a user
intentionally clicks outside the game window while holding down a button.
fix stage editor width
Merge branch 'master' of https://github.com/kpscript/pdm

Conflicts:
	assets/javascript/canvas-engine.js
optimized stage editor loading; now much, much faster
Style rework; canvas engine fixes
Merge branch 'master' into iteration4