CDB-1345 #resolve Do not memoize S3 connection when uploading imports
CDB-1358 #resolve fix importer spec runner
CDB-1362 #resolve Tables, Visualizations, DB sizes reporting

to StatsD.

Note this requires correct config values to be set on app_config.yml.
Look at config/initializers/statsd.rb for them
CDB-1376 #resolve Tune column delimiter detection for spreadsheets
CDB-1382 #resolve Do not escape twice when generating a presigned url for S3 uploads
CDB-1381 #resolve Rename indexes when renaming a table
CDB-8 #resolve Don't allow table visualizations to begin with underscores
CDB-1392 #resolve Rename sequence when renaming a table
Drop not null constraint from Tables#name_legacy
Drop indexes related to Table#name or Table#name_legacy
Fix dropping name index from user_tables
Merge remote-tracking branch 'origin/CDB-1260' into release/2.7.0
Merge remote-tracking branch 'origin/CDB-1392' into release/2.7.0
Merge remote-tracking branch 'origin/CDB-1382' into release/2.7.0
Merge remote-tracking branch 'origin/CDB-1376' into release/2.7.0
Merge remote-tracking branch 'origin/CDB-1362' into release/2.7.0
Merge remote-tracking branch 'origin/fix/CDB-1358' into release/2.7.0
Merge remote-tracking branch 'origin/CDB-1345' into release/2.7.0
Merge remote-tracking branch 'origin/fix/CDB-8' into release/2.7.0