Add basic and shaky pragma editing

Since quite a few problems are fixed by now and the program is moving
towards rudeimentary usability again it's time to add some new features
and problems!
Use per pixel scrolling in tree widget showing the DB structure

Do not scroll per item but per pixel when scrolling in the tree widget
in the DB structure tab of the main window. This makes scrolling much
more comfortable when the schema string includes line breaks.
Move content of sqlitebrowsertypes.h to sqlitedb.h