Cancel operation

[mfornet]

Right now all operations that involves running commands on the shell (compiling files, generating test cases, running solutions) other than running main solution have a friendly time limit. However a high time limit might be bad, because if there is a bug (infinite cycle, or really slow program) , extension will stop working until that command finish.

Proposal to fix. On executing a command, pop up an info box with the command that is being executed and context (running checker, running generator, etc...) And add a cancel button that allow cancelling that operation.

This way, user will have feedback about what is happening, and at the same time, the ability to stop it at any time.