Add Admin.spinnerClass() and remove hardcoded icon codes
Meta: Use the default input class in helper
Install: Fix Theme settings are not setup in InstallController

Since InstallController purposefully does not extend AppController,
`$themeSettings` view variable is not populated.
Install: Minor style fixes for buttons and input classes

Need to use span11 for inputs (instead of default class configured in theme)
here.  This is because we are using input-append addons which screws up the
form size.
Merge branch '2.1-install'

* 2.1-install:
  Install: Minor style fixes for buttons and input classes
  Install: Fix Theme settings are not setup in InstallController