performance and user experience improvements

[sbwalker]

There are a number of items in this PR:

• improved performance for module definitions and fixed siteid caching bug
• improved module deletion user experience so that a restart is not required
• improved module definition deletion to handle situation where asset manifest does not exist
• improved performance for loading themes
• improved theme deletion user experience so that a restart is not required
• improved theme deletion to handle situation where asset manifest does not exist
• added ability to specify a custom admin container for a site
• removed tenant management UI and added tenant info to Site management to reduce confusion
• changed asset manifest to use relative paths rather than absolute
• allowed modules to include an asset manifest in their nuget package
• modified localization logic so that it only sets cookie if it is null
• add first and last options to pager and made default toolbar display above grid so that position is consistent and does not move based on number of items in list
• converted menu code behind files to inline