[fixed] Include missing PropType validations

@AlexKVal has been doing som great work to clean up the large number of
linting warnings that we've been having. These have been addressed in
the commits:

6c074d8 - Temporary mute eslint react/no-did-mount-set-state warning
43f6f2e - Do not disable `setState in componentDidMount` eslint rule for docs/src
c401633 - Off superfluous 'no-script-url' for tests.
3d4cfdc - Off 'missing props validation' for tests. Removes 2 'overlay is missing in props validation' in test/OverlayMixinSpec.js.
c2e7822 - off Empty components are self-closing. <Badge></Badge> => <Badge />
658ad08 - Off only warning for ie8 special case testing. 'multiple React components in one file' I think there is no need to split ie8/src.js to several files for that.
45d172d - Off superfluous 38 warnings for examples code in docs
94a8be4 - fix for singlequote warning
82d4a42 - Define type for `title` property in PageItem
2cebc2c - Define type for `collapsable` property in CollapsableNav
587a6a9 - Define type for `interval` property in Carousel