Schema version for the next release

[julianbrost]

Currently, there is some chaos with schema upgrades in 1.1.1.sql and 1.2.0.sql which has to be cleaned up for the next release.

Tasks:

• Ensure that the file name will be correct for the next release.
• Bump the schema version stored inside the database (Write a hint for empty arrays/dicts into customvar_flat #601 violates constraints of the old schema)

[julianbrost]

According to the current plan, this will be the schema changes:

• schema: notification: enlarge name and name_ci 255 -> 767 #584
• Write a hint for empty arrays/dicts into customvar_flat #601
• Prepare history table for order by event_time desc, event_type desc #614
• schema: Add missing indices to hostgroup and servicegroup #616
• schema: Add new index for customvar_flat #617

At least #601 is incompatible in the sense that without the schema upgrade applied, it can trigger constraint violations, thus we should increment the schema version so that Icinga DB will complain on startup if the schema upgrade wasn't applied.