Fallback to loading theme icons from resources

Since not all platforms support theme icons, we need to pack
them into resources and fallback to that resource theme.

There seems to be a bug in Qt
(https://bugreports.qt-project.org/browse/QTBUG-16697), thus
default theme name (hicolor) does not work. So we test for
'window-close' theme icon on startup and if not found, set theme
name to 'subsurface'

Signed-off-by: Sergey Starosek <sergey.starosek@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Fix date and time l10n

QDateTime::toString(const QString & format) uses system locale
for month and day names.

In order to get localized month and day names for user-choosen locale
use QLocale::toString(const QDateTime & datetime, const QString & format)
instead.

Signed-off-by: Sergey Starosek <sergey.starosek@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Rename slot to get rid of auto-connect warning

Signed-off-by: Sergey Starosek <sergey.starosek@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Use date / time entry for start time of planned dive

This is not hooked up, yet, just the UI change.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Planner: implement sane way to set the start time of the planned dive

This uses the same widgets we use on the maintab.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Merge branch 'fixPlannerStartTime'
Planner: small fixes for the UI

This way the calendar looks more "natural".
And a typo fix.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>