Add "Create Antisense Strand" icon on the toolbar

[ljubica-milovic]

Background

Because the functionality of adding antisense chains is an important one and a commonly used one, there should be a "Create Antisense Strand" toolbar icon.

Requirements

1. A toolbar icon should be added bellow the bond tool, and separated from it by a line.

Currently, a line separates the bond tool and hand, select, and erase tools.

2. The preview tooltip should be "Create Antisense Strand", and the hotkey should be Alt + A (Option + A for MacOS).

3. When an appropriate monomers are selected the tool should be enabled.

Appropriate selection described in the ticket #5678, under requirement 1 and its sub requirements.

4. When no monomers are selected, or the selected monomers are not appropriate, the tool should be disabled.

5. When the icon is clicked, the antisense chain should be created following the logic described in the ticket #5678 under requirement 2 and its its sub requirements and layouted based on the mode (flex: #5678, snake: #5712, sequence (old): #5925, sequence (new): #5942).

UX
TBD