Physical units tracking

Added support for physical units tracking in plots
Started - settings dialogs

Started implementing settings dialogs.
Default units dialog.
TODO: general settings dialog
bug fixes

Fixed bugs with physical units
Main settings dialog
Added saving and loading default units

Default units can be defined in the main configuration file.
Small fixes
Units management fixes

- Fixed simplification of units. Now simplifies complementary default
units.
- Fixed bug with units and post-processing canvases, where new canvases
overwrote old canvases units.
Version update
Bug fixes

Scan hardware and reset hardware were still based on some broken old
code.
Version update
Added generic save event
Help menu

Added help menu with link to online doc
Version update
Merge branch 'master' of https://github.com/vpaeder/terapy