#39 User should be able to start only one instance of SourceLine application

[Alex Chmykhalo]

• User should be able to start only one instance of SourceLine application
• When user will run SourceLine second time (and there is already running SourceLine instance):
  • Second instance should exit without loading
  • First instance of application that is already running should popup on screen (if it was hidden behind other windows or minimized)
• Use QtSingleApplication from src/app/3rdparty/ directory (master branch of SL project)
• Create separate SourceLineApplication class and inherit it from QtSingleApplicatino class

[Alex Chmykhalo]

Please, update status of the ticket.