Fix additive groups export without parent

fixes #2670
Add doc/export.md explaining the 2.x migration export and best practices

fixes #2773
doc/export.md: Fix formatting

refs #2773
LConfDeployIcinga2.sh: Add support for Icinga2 2.2

fixes #2777
icinga2: Notification Migration: counts must go up on 1) contacts 2) commands

refs #2664
Remove event/notification command default USER mapping
Fix escape_str()
Icinga 2: Export enable_{active,passive}_checks attributes

fixes #2702
icinga2: Fixed notification filters (#2759, #2765, #2663)

fixes #2759
fixes #2765
fixes #2663
Icinga 2: Fix missing 'check_period' attribute export

refs #2750
icinga2: added enable_perfdata option (#2708)

fixes #2708
Icinga 2: Add missing notification interval, fix period for host notifications

refs #2750
Icinga2: Fix duplicate notification object generation

fixes #2664
Icinga 2: Add note about unsupported migration attributes for contacts

fixes #2750
icinga2: map icinga1 contactgroups to icinga2 usergroups

fixes #2769
Icinga 2: Add service eventhandler argument support

fixes #2767
Icinga 2: Add missing host eventhandlers w/ arguments

fixes #2781
Icinga2: Fix duplicate notification object generation for service

refs #2664
icinga2: added mapping from icinga1 contactgroup members to icinga2 usergroups

fixes #2748
Icinga2: Add a log message if there are no notification commands defined

fixes #2668