Add 'activate' and 'deactivate' plugin hooks.  Issue #349
Adds output formats list to items/show view.

Omeka provides links to its various output formats on the items/browse view.
(This was added in ae45808 in response to ticket #373.) Those same formats
are also generated for individual items. This change simply adds links to
those views on the core items/show view.
Use 'type' key for item type field in advanced search.

Changes the key on $_REQUEST to 'type' instead of 'item-type-search', so that
the item type field is corrected selected if that parameter is set on the
advanced search page.
Adds output format list to items/browse.
Normalized function used to get derivative filename.
Add element set POST.
Add horizontal rules to distinguish between multiple texts for an element.
Fix variable name.
Fix logic bug/notice in Tag mixin.
Fix bugs and tests from some API changes.
Add item type POST.
Use absolute positioning on content nav if the window is shorter than the nav. Fix #519.
Remove version resource.
Validate record before validating user.
Add POST file.
POST method must not have parameters.
Require synchronous job for API file uploads.
Set element text data to file on POST.
Search plugins by name.
Merge pull request #551 from Daniel-KM/get_derivative_filename

Normalized function used to get derivative filename.