*boruta_modbus: change def registers timeout

defualt value for timing out registers in 1 minute
(instead of no time out at all)
*wx/draw3: show values diff for double cursor

while in double coursor info widget also shows difference
between valus at the beginning and end of range
*wx/draw3: small new feature

Pressing right mouse button on graphs widgets switches
widget to double cursor mode. Moving the mouse, with
right button still pressed, makes the graph cursor
to follow mouse pointer. When the right mouse button is
relased widget switches back to non-double cursor mode.

+ 2-3 compilation warnings removed
Merge branch 'master' of https://github.com/Newterm/szarp