Stop skin map calculation as soon as we know it won't work

[Ed McDonagh]

Currently the skin map routines attempt to make a skin map even when we know it won't work/won't be right.

I would like for it to (by default at least) stop at the earliest opportunity. For example if it is not a Siemens unit, or there are non-Cu filtrations in use.

In the situation where you have a mix of Siemens systems and others, you may want skin maps switched on but not to slow the system down attempting failed calculations for the other systems.

I can also see that you may want to make it easy to let them calculate for anyone who wants to investigate how to develop the software further, but that shouldn't be the default situation.

I don't know if this is in @dplatten's code or the original @jacole openSkin code. Maybe it could be achieved by creating a dummy calc file when testing for height and weight etc in rf_detail_view_skin_map if we also test for Siemens etc in that section.

Also refs #562 (making messages more explicit), #557 (missing patient modifier) and #558 (missing kVp data).

I'd also appreciate @LuukO's view on this.

[Ed McDonagh]

Merged in Issue558SkinMapStopsOnNoKvp (pull request #127)

Fixes #558 Openskin: calculation stops with error if kVp is missing

I'd like to see further changes to this code as per ref #563, but this PR is better than the current code for several reasons so we'll merge this in :-)

→ <<cset 6559337e3596>>

[Ed McDonagh]

Pushing this issue to a future release - it isn't essential for 0.8.0. Will be very slightly mitigated by a better error message as per issue ref #562