Platform startup now reads the used database driver from <ws>/db.ini

Platform startup now reads the used database driver from <ws>/db.ini

Previously it was possible to use the wrong database driver for a
workspace if the default driver was changed in the code. Now,
SimanticsPlatform.setupDatabase will read the database driver used for
the opened workspace from an ini file <workspace>/db.ini. If the file
does not exist, it will write it with the following data:
[driver]
id = <database-id-value>

refs #6747

Change-Id: Ie304b480095657e25e694a81cdd5085a4d2c17e9