Added missing include
pv::view::View::get_time_extents: Assume samplerate is 1 if given an invalid value

Fixes #278
pv::view::View::zoom: Removed duplicated scale clamping
pv::view::View::zoom_fit: clamp the scale between MaxScale and MinScale

Fixes #278
pv::view::View::set_zoom: Added doxygen comment
QWellArray: removed unused destructor
QWellArray: Removed dead code
QWellArray: Removed QT_NO_MENU functionality

This fixes bug #265
Removed duplicated source listing of wellarray.cpp
SigSession: Tidied update_signals
SigSession: Added signal_from_probe
LogicSignal: Tidyup boost references
Added AnalogSignal::analog_data accessor function
Feed analog data into separate deinterleaved analog data objects per channel
Created pv::widgets::SampleTimingWidget, and ported the SamplingBar to use it.

This widget allows the user to edit a sample timing value either from
a list of options, or as an value with a min/max/step, or as read
only, or hidden.
Use a SweepTimingWidget for sample count limit.
Show sample count selector only if setting supported.
No longer need to set sample limit on session start.
Wait until SDI is set before updating sweep timing widgets.
Commit sample count after setting default.