[Debugger] Use a separate mutex lock for toggling breakpoints

Hopefully fixes bug #7143
[Debugger] actually, fuck it. kill the mutex lock.

The locking was pointless - it'd need to be inside
BreakpointStore.Toggle() to have any value anyway.
[Deps] Bump md-addins.
[Deps] Bump md-addins to fix the build.
Fixed disassembly view Version Control Menu crash.

This fixes Disassembly window from crashing MonoDevelop due to it being marked
as a file.
Also removed some redundant namespace usages.
Merge pull request #294 from Therzok/fixRegressions

Fixed disassembly view Version Control Menu crash.