Clean up Icinga timezone definitions

* Made PDT actually PDT rather than PST
* Added real PST
* Added CEST
* Added EDT and EST_early to complement EDT_early and EST
* Fix typos (s/til/till/g)

Note that this will affect people whose paging hours are set to PDT.
Right now, PDT means 8am-midnight in winter and 7am-11pm in summer,
which is broken. This commit changes PDT to actually mean 8am-midnight
in summer; once DST goes away on Sunday every PDT contact should be set
to PST so as to maintain the 8am-midnight behavior.

Change-Id: I5d00bfebc818d37f9e6f7ac20a00f8d07f830d8e
Merge "Clean up Icinga timezone definitions" into production