History Limiter Custom

A personal edit of nschneirov's History Limiter put up to share.
Overall the logic remain unchanged from the original version.

Main changes:
- code reworks to eliminate need for jQuery and to facilitate manifest ver 2
- event page enabled
- no changes to logic, no new functions

The main aim of this edit is to make it event page enabled so it unloads when not needed thus saving memory.

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CHANGELOG:

1.2 [21/04/2018]
- back to using a set button to overcome the premature clear
- some minor UI changes

1.1.1 [10/05/2014]
- history will be trimmed right after the day value is edited

1.1 [27/04/2014]
- tidying and restructuring of code
- changed options page to auto save
- added textfield number check
- added working 0 days mode (no history)