Create reindex.py

Based on annotator-store's reindex[er].py, but with our models, and also
configuring settings (custom analysers etc.)
Give helpful message on MergeMappingException
Add command reindex to script.py
Update warning message
Fix behaviour on error
log.fatal -> log.critical
Simplify reindexer.py using annotator-v0.13
Merge pull request #1715 from Treora/reindex

Create reindex.py, add warning on mapping conflict