Add breakpoints in the script editor

[ambrosiogabe]

Add the ability to set a breakpoint via the text editor and halt the script when that breakpoint is hit. This task will be completed when:

• You can add a breakpoint in the left margin
• The script pauses at the breakpoint
• You can step a single line of code
• You can resume execution of the script

Script inspection, watch windows, etc will be added in other issues.