-Created SearchFilters class, which we'll use to store and generate the search query strings for the filtered search.
-Changed the way MokapBackend servlet manages the parameters, using the new SearchFilters class
-Merged the searchByString methods in DatastoreAccess class into one, using the SearchFilters class
-Modified MokapSearchController class to fit the new SearchFilters class
-Made the controller variables in MockapBackend servlet local
-Changed the tempFileName generation to improve performance (minor fix)
-Changed visibility of isValidKey in ApiKeyVerifier class to private because it is only used locally
-Fixed some javadoc around the project
Class with static fields for referring the subpaths of any uploaded zip (contents, descriptor, etc) and also methods for validity checking
ServerReturnMessages class with all return messages of the server in a centralized place. Also: ServerError utility exception
Using new server errors
Making use of UploadZipStructure
Unrelated to this PR - Removing a pending "entityRef" reference
Merge pull request #20 from jtorrente/servererrors

Improved error management
Merge branch 'master' of https://github.com/mdebenito/mokap-backend into fiteredsearch

Conflicts:
	MokapBackend/src/main/java/es/eucm/mokap/backend/controller/search/MokapSearchController.java
Solved some merge conflicts
-Fixed small bug that prevented thumbnails to be retrieved in search responses
-Added a searchString field to the response that represents the string used in the query to the database (for debug purposes and highly informative IMO)
-Added toString method to SearchFilters class

Some JDoc pending, the filtered search is working.
Small JDoc addition
Another step towards protecting mokap-backend against API changes
Addressed the comments in the PR
Removed unused import
Merge pull request #25 from jtorrente/requestfields

Another step towards protecting mokap-backend against API changes
Revert "Another step towards protecting mokap-backend against API changes"
Merge pull request #27 from e-ucm/revert-25-requestfields

Revert "Another step towards protecting mokap-backend against API change...
Merge pull request #22 from mdebenito/fiteredsearch

Filtered Search
Added formatter and license header plugins.
Code formatted and license headers added