feat(search): add search resource

search resource will be used for searching ingest/content/etc together.

SD-1057

Conflicts:
	superdesk/__init__.py
Merge remote-tracking branch 'siva/master'
[SD-945] Improvements:
1. Reusing the variables instead of asking the dict() again.
2. Refactored few lines to a function().
3. Adding a behave test for testing Metadata
[SD-1051] Second Issue is fixed
[SD-945] Anpa Category has to be dict type, not string