Rotate all active-write indexes UI option

When spinning up multiple indexes for different log types/sources, it would be nice to be able to perform maintenance functions across 'all indexes' at once.

The most obvious are the two available options: recalculate index and rotate active writes.

## Expected Behavior
On the Indicies overview page, have a maintenance option to impact all available index sets.

## Current Behavior
Each maintenance action must be performed per-index.

## Possible Solution
Provide a UI element or method of multi-select on index management to mass-perform actions.

## Context
During maintenance / troubleshooting it may become nessessary to perform maintenance actions on all index sets. This is very 'click-intensive'.

* Graylog Version: 3.0