Chart Dates: Part 3b of 3

Added chart date selection to the CP chart.
Still need to add this to;
    - Summary
    - Histogram
Chart Dates: Part 3c of 3

Added chart date selection to the Summary chart.
Still need to add this to;
        - Histogram
Fix date settings needed a restart

To get the date settings to register user interaction
you needed to restart gc after adding the chart. This
was caused by an initialisation error, setting the active
flag to true on object creation -- it should have been
set to false.
Chart Dates: Part 3d of 3 (final)

Added chart date selection to the Histogram chart.
This now completes the updates to enable custom date
ranges to be defined in charts that support date
ranges.

Any further 'ideas' for setting custom ranges can be
added into the DateRangeEdit widget and will be re-used
across all the charts.

Fixes #417
Fix KML needing boost in gcconfig and src.pro

Fixes #421
Edit times using a QTimeEdit in Metadata

When overriding the duration, time riding and other
time based metrics in the metadata screen it asks
the user for the time in seconds.

This update offers a QTimeEdit to edit them, a little
more user friendly.

Fixes #422
clang 4.1 fixups

remove casts to keep clang 4.1 happy on
Mac OS X. Now produces a number of warnings
on clang 4.0.

Fixes #420