Kairosdb datasource

Hi !
This is a full support of the kairosDB datasource with a pretty complete input validation. Some issues with CORS have been noticed on version 0.9.3 of KairosDB, so version 0.9.4 is recommended.
Possible enhancement would be to add the display of non-numerical series (possible in KairosDB since 0.9.4) as events.