Some minor improvements

- Add grib file date/time information in the dialog caption
- Correct invisible overlay message over writing when several overlays
are selected
- Correct display problem in grib dialog
_ Remove useless code
Correct dysfunctions & compability interpolate / no interpolate logics

- 'next' & 'prev' buttons do not work with slices higher than file time
step
- Correct wrong results when interpolation factors (slices per update /
per hours) are not miltiple or submultiple of hours
- Ensure accuracy when interpolation situation(FS#1087)
- Correct dysfuntion with Linux (combobox doesn't reacts the same way as
with Windows)
Correct String translation linked to 'some minor improvements'  commit

sorry for this forgetting
Merge remote-tracking branch 'upstream1/master'
Add "convective available potential energy" (CAPE)  parameter
Correct interpolation when data missing in part of overlay(waves  or current)
Apply immediately  "hight def" & "smooth colors" setting changes
Correct related data display in grib dialog when starting with "copy first missing records" unchecked
Merge pull request #79 from Ptizef/master

Some minor improvements
Correct occasional fault on SENC file creation, Windows.  (FS#1213)
Improve vector chart depth formatting for units = "feet"
Merge branch 'master' of https://github.com/OpenCPN/OpenCPN