Copy missing indexes in history table

Creation of a method that copy the temporal table indexes to the history table if they does not exist.
Method/variable renaming + Fix for change_table

Method "copy_temporal_indexes_to_history_after_change_table_to_temporal":
- Rename the method to "copy_indexes_to_history_from_temporal".
- Rename the local variable from "temporal_index" to "index"
- Add specifications
Method "change_table":
- Call the method "copy_indexes_to_history_from_temporal" to copy the indexes in history for the tables using indexes before the temporalizing.
Merge branch 'Copy-missing-indexes-in-history-table' of git://github.com/Arkanys/chronomodel into Arkanys-Copy-missing-indexes-in-history-table

* 'Copy-missing-indexes-in-history-table' of git://github.com/Arkanys/chronomodel:
  Method/variable renaming + Fix for change_table
  Copy missing indexes in history table
:sweat: Fix stupidity in checking indexes existance
:relaxed: Refactor @Arkanys' code and add specs (closes #21)