Version 3.1.2

This is a major stability improvement, resolving several issues that came to light since release 3.1.1.
Fixes bug #468 broken remove constraint buttons in simultaneous/constrained fitting panel
Fixes bug #474 resulting from changes in 3.1.1 that had introduced an error in the high-Q of slit-smeared models
Fixes bug #478 which would cause wx to run out of IDs and result in SasView crashing even if left alone
Fixes bug #479 missing help button on simultaneous/constrained fit page
Fixes bug #480 GUI resizing issues on simultaneous fit page
Fixes bug #486 broken Report Results
Fixes bug #488 redraw issues in fit page