Reimplement file save using the srzip output module.

This should fix (part of) bug #451.
LogicSignal: Removed trailing whitespace
LogicSignal: Tidied populate_popup_form is_checked
LogicSignal: Replaced TRUE/FALSE with true/false
SigSession: Replaced do { } while(0) with { }
Signal: Added a reference to _session
SigSession: Renamed get_device to device
StoreSession: Removed commented code
.gitignore: Ignore vim .swo files
SigSession: Made _sr_session non-static
SigSession: Added DeviceManager accessor functions
LogicSignal: Ported triggers to new API

This fixes bugs #448 and #452.
View: Update view on capture state change
.gitignore: Ignore QtCreator generated files.
SamplingBar: Add Space as a shortcut to Run/Stop.
Update description for Trace::get_label_rect()
DecodeTrace: Turn row_height and text_height into class members
DecodeTrace: Refactor sample helpers and simplify method calls
Trace: Introduce hover_point_changed()
DecodeTrace: Provide tool tips for annotations