Added option to disable cache_clearer

[Spea]

Added a new option auto_clear_cache so the cache_clearer can be disabled.

This PR fixes #89

[travisbot]

This pull request passes (merged 939af6f1 into e01cb51).

[lsmith77]

please also remove the liip_imagine.cache.clearer.class parameter from this file

[Spea]

Done

[travisbot]

This pull request passes (merged c4a6ccb into e01cb51).

[lsmith77]

thought about this some more .. maybe auto_clear_cache should better be called clear_cacher?

[Spea]

not sure about this, in my opinion auto_clear_cache is easier to understand

[lsmith77]

but it makes it sound like there is some complex logic that triggers a clear "automatically"

[Spea]

you're right, guess we should change it then. shall i create another PR for this?

[lsmith77]

that would be very much appreciated!

[Spea]

btw. i think you meant cache_clearer instead of clear_cacher, didn't you?

[lsmith77]

yes :)