Removed cotire

cotire has proven itself to be counter-productive. It rebuilts the pre-compiled
header after any header in pulseview is modified causes a complete rebuild of
all of PulseView. Also, the pre-compiled header contains a union of all the
includes of all source files, which masks errors where source files are missing
needed includes.
LogicSignal: Added trigger markers
RowItem: Bundled painting parameters into RowItemPaintParams
Trace: Make paint_axis take RowItemPaintParams
.gitignore: Added .ninja_deps
RowItemPaintParams: Bundled scale and offset
RowItemParams: Added font and text_height
Session: Renamed files to match class name
Renamed pv::data::Analog::get_snapshots and Logic::get_snapshots
DecoderStack: Emancipate from SignalData
SignalData: Added snapshots accessor method
SignalData: Moved start_time into Snapshot
SignalData: Moved samplerate into Snapshot
Snapshot: Renamed to Segment
Ruler: Moved calculate_tick_spacing into View
DecodeTrace: Removed incorrect use of get_text_colour
Trace: Moved get_text_colour into SelectableItem
Cursor: Moved paint_label into TimeMarker
TimeMarker: Added default get_label_rect implementation