Allow 'refresh_immune_slices'

[ratb3rt]

Ref #2958 , add a 'refresh_immune_slices' property to dashboards. Any slice ids listed will not be included in an automatic dashboard refresh.
I chose to exclude rather than include to be consist with filter_immune_slices.

[mistercrunch]

LGTM in general except that the setting name is not specific enough, and you should add an entry in the docs/faq.rst

[mistercrunch]

Also you can make sure you pass the build before sending in the PR by setting up travis-ci against your fork. It's really easy to setup and will run a build for each new push on your repo.

[ratb3rt]

Updated to 'timed_refresh_immune_slices' in latest commit, added usage to faq.rst

[ratb3rt]

Any additional reviews on this PR?

[coveralls]

Coverage increased (+0.002%) to 69.3% when pulling db7a64d on RichRadics:refresh_immune into 90592d3 on apache:master.

[coveralls]

Coverage increased (+0.002%) to 69.3% when pulling db7a64d on RichRadics:refresh_immune into 90592d3 on apache:master.