Add new function to DBBrowserDB which creates a new table

Add a new function to the DBBrowserDB class which creates a new table.

Use this function in most places where a table needs to be created.
Silence to debug messages
Rewrite the create index dialog

Use Qt Designer for the create index dialog.

Change the layout of the create index dialog completely to be easier to
use and more powerful.

Rewrite most of the index creation code to be easier to understand and
more flexible.
Rename dialog files and classes

Rename the files and classes for the dialogs to share all the same
naming pattern. This should make navigation in the code a bit easier.
Do not include dialogs not rewritten yet; they'll be edited as they are
redesigned.
Remove the modified flag in the EditTableDialog

Remove the flag storing the mofification status in the edit table
dialog. It's only been used in one place and there it was not even
really needed - so why bothering updating and maintaining it?