[ticket/11369] Reverting migration throws error

String is attempted to be unserialized

PHPBB3-11369
[ticket/11370] Effectively installed migrations not inserted into table

insert_migration() function now handles inserting/updating

Move all insert/update code to insert_migration() function to prevent this from occurring again.

PHPBB3-11370
Merge remote-tracking branch 'EXreaction/ticket/11369' into develop

# By Nathaniel Guse
# Via Nathaniel Guse
* EXreaction/ticket/11369:
  [ticket/11369] Reverting migration throws error
Merge remote-tracking branch 'EXreaction/ticket/11370' into develop

# By Nathaniel Guse
# Via Nathaniel Guse
* EXreaction/ticket/11370:
  [ticket/11370] Effectively installed migrations not inserted into table
Merge branch 'develop' of github.com:phpbb/phpbb3 into ticket/11103

# By Nathaniel Guse
# Via David King (2) and Nathaniel Guse (1)
* 'develop' of github.com:phpbb/phpbb3:
  [ticket/11370] Effectively installed migrations not inserted into table
  [ticket/11369] Reverting migration throws error