Feature/imagex search

## Ready State: NO

This pull request is related to the following JIRA tickets: https://imagex.atlassian.net/browse/LDC-121

Based on the Linux jira task above and general imagex_search feature has been created which contains:
- Module dependencies: search_api, search_api_sorts, facetapi
- Search Result view mode (field displays not included, just provides the view mode) (done using entity_view_modes module)
- Search result image style (common thumbnail size)
- Basic default /search page & view, keyword search only & search sorts & content type facets
- Default search index settings & test server (relates to view)


## Requirements & Dependencies

* Requires these commits to be patched into imagex_installkit: https://github.com/thomjjames/imagex_installkit/commit/e350f96c2c95a9904cbb2353a0e735e5e78d885f
https://github.com/thomjjames/imagex_installkit/commit/621e6e50f09e48d7820591ff54198740fd33ef93 (added to allow test server by default)

## Deployment Instructions

* Merge code.
* Enable imagex_search feature

## Usage/Test Instructions

* Enable imagex_search feature
* Create some test content of various content types
* Enable search_api_db module (provides a test search server for testing only (without needing Solr) hence why its not a dependency, the server can be deleted & the module disabled if required)
* Go to /admin/config/search/search_api/index/default_node_index/status and:
  * ensure Status: The index is currently enabled.
  * "re-index" the index so the test content is picked up
* Go to /search and ensure: 
  * No results, sorts or facets are shown before a search is inputted
  * After searching the left sidebar contains & are functional: Keyword search, number of items to display, sort by (Date created, Relevance, Alphabetically) & Filtered by (content types)
  * After searching the main column contains & are functional: title, total results found count, total pages & the current page and the search results 

NOTE: the Search Result view mode is merely provided as a base & not set up per content type which maybe site specific, also its not possible to set a default for all content types

NOTE: I was unable to make a fresh installation to test this deployment on so please let me know if you hit any errors.

## Site Specific Overrides

As the search api views integration does not allow the search index to use for a search to be changed after initial saving of a view (index is set as base table) this feature would need to be build on top of/overridden for site specific searches rather than being independent.