Dynamically scales DPI of TeX by area, fixes #75.
Added setting for presentationMode
Connected handlers for presentationMode
Mapped Up/Dn to PgUp/PgDn for presentation mode
Added presentation mode to Actions
Added GROUP_PRESENTATION_MODE to Actions
Fixed typo in setViewPresentationMode
Merge branch 'master' into addpoppler
Merge branch 'addpoppler' into glib_new
Gave MainWindow control over all keypress events

This allows MainWindow to filter through for events that should apply
everywhere. Glade was grabbing Up and Down. This returns control to
scroll through the worksheet. Fixes bug #74.
Gave control back to selections
Merge branch 'master' into addpoppler
Gave control to text editor
Merge branch 'master' into addpoppler
Merge branch 'addpoppler' into glib_new
Recovered Presentation Mode
Merge branch 'master' into addpoppler
Merge branch 'addpoppler' into glib_new
Finer zoom control and Vertical Spacing

The zoom in/out is now much finer, and there is now vertical spacing
between slides as well as above and below when selected.
Made slides center in presentation mode.