GMediaDB Updates and GMediaMP tag editing

There is now a new tag editor interface for the GMediaMP application.  I created a class that handles all the details, now it should be simple work to just hook up all the different library panes.  Currently the TV Shows pane is hooked up and working.  It provides a simple interface that makes it easy to add, remove or update tags.

A lot of changes have happened to the backend as well.  There are two main big changes.  First the gmediadb_update_entry function gained the capability to delete tags.  In earlier versions you could only add and change tags.  Now to delete a tag you give the tag like normal but specify a value of NULL.  The function will take this to mean the tag should be deleted and it will remove it from the database for that entry.  The second big change is for all the methods to get tags for entries.  Now if you pass in a NULL value for the tag array, the function will return all the possible tags for a given entry.  And because the functions still only return a string array for each entry, the keys and values are multiplexed together into the same array.  So the resulting array from one of these calls will look something like tag1, val1, tag2, val2, …, NULL.  When the application specifies a tag array, the returned array still only contains the values.  This change allows the application to either retrieve as many tags as it needs or all of them.  With these changes, the library is turning in to something very functional and useful to applications.