Bug 1465107: Use Bootstrap CSS Framework

1. Moving all the pluginfiles for themes into a "plugintype" directory. So
e.g. htdocs/theme/raw/blocktype/clippy/templates/clippy.tpl becomes
htdocs/theme/raw/plugintype/blocktype/clippy/templates/clippy.tpl.

2. Moving all the things under "static" in themes, to the theme's root.
So htdocs/theme/raw/static/style/style.css becomes htdocs/theme/raw/style.css
and htdocs/theme/raw/blocktype/clippy/static/images/clippy.png becomes
htdocs/theme/raw/blocktype/clippy/images/clippy.png

This should make things a little clearer for new theme devs. It's
still confusing to have all the images scattered throughout the plugin
subdirectories, but that's hard to fix because we treat the asset type
as part of the filename, e.g. $THEME->get_url('style/style.css') instead
of $THEME->get_url('style', 'style.css');

Change-Id: Ia216a40fb72624113e56d7eac698bfeb5adafcf0