fix: invert selection is wrong

[rh-anocca]

Issue

The new invert selection isn't quite right; there are three types of inversion possible with DNA.

1. Select the unselected, deselect the original, but maintain the direction
2. Select the unselected, deselect the original, but invert the direction (i.e. select opposite direction)
3. Select the currently selected, but invert the direction.

Right now, clicking "invert" conducts the option 2, but the more intuitive version is 1.

Steps to reproduce

• Go to any sequence viewer
• Select at least 1 region.
• Click the invert button
• The inverted selection will be made BUT it is selecting in the opposite direction. i.e. reverse strand, when original was forward.

Expected behaviour

Default behaviour is to use option 1.

Ideal scenario is that the use has the option to do all three options (drop down menu?)