Added expiretime acknowledgements to host and service grids

This feature adds an option to enter a duration in hours/minutes for expiretime
acknowledgement instead of the exact date/time. To choose the default checked
radio button ("for" or "until") there is now an parameter in icingaCommands.xml
for COMMAND_EXPIRETIME (defaultChecked="for" or defaultChecked="until").

refs #4194

Signed-off-by: Markus Frosch <markus@lazyfrosch.de>
Fix acknowledgements with expiretime icon for problem services

refs #4194
Tidied up CommandHandler.js for jshint warnings

refs #4194
Merge branch 'feature/acknowledgements-expiretime-4194' into next