Dashboard list pagination preference not saved

Pagination on Dashboard page preference is not saved anywhere. You can change the number of dashboards listed( 10 / 50 / 100 ) but that preference is not retained once you navigate away from the dashboards.

## Expected Behavior
This should be a user-level preference or capable of being set globally as a default at system level.

## Current Behavior
Pagination preferences can be changed but are forgotten immediately on page load.

## Possible Solution
Save user preference or make a system level configuration option to force a different pagination default.

## Steps to Reproduce (for bugs)
1. Open dashboard list
2. Change pagination limit(show dropdown number)
3. Navigate away and back to dashboard list
4. Observe the default pagination value setting is back.

## Context
Annoying to change every time you view dashboard if you want to list more at once.

## Your Environment
* Graylog Version: 3.2.1