Let the reporting tool save GitHub user name

@evgeniy-ADG commented on [Thu Mar 15 2018](https://github.com/AdguardTeam/AdguardForWindows/issues/2150)

It'll make the tool more user friendly to those who use it quite often.


### Expected behavior

The account name is saved so that you don't have to re-enter it each time

### Actual behavior

You need to put your GitHub account name each time you report a problem

### Your environment

* Environment name and version (e.g. Chrome 59): any
* Operating system and version (e.g. Windows 10, v.1703, build 15063.413): any