TEIIDDES-2120: Stop relocating xsd files

* FileUtil
* mime.types
 * Function for guessing the file type of a file

* VdbMigrateXsdFilesMarkerResolution
 * No need to migrate xsd files anymore. Just need to open the vdb and
   resave it in order to fix a vdb

* VdbEditor
 * Adds a tab panel for displaying schema files since they are now
   separate from both the models and other files

* Vdb
 * Splits the entries into 3 sets, file, udf jar and schema
 * Automatically detect whether xsds are contained in the model entries of
   the vdb manifest or entries and deal with them separately.
 * This essentially fixes a vdb if it is the 'old' type
 * No longer need migrate method since the xsd files are not actually
   being relocated.

* VdbEntry
 * If the file has no contents and a null stream is produced then return
   -1 for the checksum rather than allowing a NPE

* VdbIndexedEntry
 * Abstract parent class for both VdbModelEntry and VdbSchemaEntry that
   is concerned with managing the indexes of these types of entry

* VdbSchemaEntry
 * Own class explicitly for schemas delineating from both model and file
   entries.
Merge pull request #375 from phantomjinx/TEIIDDES-2120

Teiiddes 2120