Right-click popup menu in ScaledView/Bandview/ROIView

[ypnos]

ScaledView should have a popup menu with following items:

• Scale best fit (internal scale 1), this also centers view like it currently does
• Scale 100% (1:1 pixmap, not the internal scale 1)

The method that produces the menu should be overloadable.

ROIView should overload it to replace with a menu that contains:

• Apply
• Reset

BandView should overload it to enhance the menu with:

• The three modes to be selected, checkable so indicating current mode
• In the future maybe additional items per-mode

Right now we have modes in bandview that use right click, so there obviously the menu method would not be called.

Use QActions where appropriate.

[ypnos]

Merged #21