Refactored language handling in BaseController. (closes #344)
Increased thread-safety for Site.current.
Refactored PagesController#load_page.
Introduce host aliases for sites.

This allows the site admin to optionally enter a list of whitespace-separated alias hosts for sites, making individual sites available to more than a single host.

In addition, each site now has the option to enforce its primary host name as its canonical URL by way of redirection.
Merge pull request #345 from magiclabs/feature/site_aliases

Introduce host aliases for sites.
Renaming Site attributes
Bump version to 2.5.0.b5
Adds errors module for custom error classes.
GUI refactoring:

- Help texts for resource attributes
- Partial for each resource attribute type
- Auto full width form elements
- Form foot note redesign
Compressed migrations for Alchemy 2.4
Fixes specs for resource_window_size and picture library tagging integration.
Bump version to 2.5.0.b6
Imports pictures and attachments via rsync. Closes #346
Only import the database from primary db server.
Use standard ssh port for rsync, if no port is defined.
Fixes bug in cap task that only imported pictures.
Corrected comments for #page_selector helper method.
Made validation of image format case insensitive