Refactor URL templates and directory structures

Templates:

* rename main -> central
* rename large -> local
* remove the 'small' template

Reasoning being that we will only separate the central site from local
sites, but not small/large local sites, in the URL template.

Further differences will be made on a content-level, not URL template
level.

js:

* move custom libraries to lib/ subfolder
* move public scripts to public/ subfolder
* move admin/public common scripts to common/ subfolder

LESS:

* rename main -> public
Restructure image directory hierarchy

* admin
* public
* common
* icons
Merge branch 'refactor'