Remove unneeded ;
Store last selected preset name.

This will be used to be able to update a preset.
Skip prefix before any tag when looking for a preset name.
Add support for updating a preset with current values.
New routine dt_gui_store_last_preset to share code.
Record last preset name when creating a new one.

This fixes a usablility issue where it was proposed to update the
preset selected before the newly created one. It was then possible
to erase an old preset.
convert blending params in presets to current version
check legacy_params return value and fix memleak in init_presets function
fix more memleaks in init_presets with hanatos's help
init_presets: handle old presets with no blending params
Add whitespace to match master to prevent future cherrypicks from breaking