Split themes into theme/ and template/

Themes were way too broad. Now, the theme is the actual default theme
and the railtie was removed from the themes/ folder. I also moved
themes/template to template as this is really only a template for
people using 'ecrire new project_name'
Added template folder
Railtie should belongs to Ecrire
Removed the default folder
Readded theme
Removed Google Analytics
Renamed path from theme:* to user:* and also monkey patched AR
initializer

I renamed the path because it used to be there to create multiple
themes. Right now, only 1 theme is supported at any given time. Also,
since the railtie is now a descendent of Ecrire, it made more sense that
way.

I also monkey patched AR::Railtie.initializers to not crash when a
database cannot be initiated. Instead, if there's no database, the
system theme is used to let the user know he needs to configure his
database.

This fix #38