[UC4] Adding of breakpoints

[Mykola Baranov]

Description: It's very convenient to add breakpoints by clicking on the left of text editor: user clicked in front of certain line where he wants to set new breakpoint or delete old. In order to prevent collision between setting breakpoint and going to error item in output panel we should use alt modifier to set breakpoint.

Basic Flow:

1. User clicked in front of line number 'n'
2. Breakpoint setted to line 'n'. Icon of breakpoint appears in front of line number 'n'.

Alternative Flows:
2a. Breakpoint was already setted to line 'n'.

• 2a1. Breakpoint deleted from line 'n'.