Updated famous-flex-global.js + various improvements/fixes

New:

• Added option overscroll to ScrollController/FlexScrollView for disabling overscroll behaviour.
• Added cells option to CollectionLayout and deprecated GridLayout.
• Added .get function for getting a renderable by its id or index.
• Added .replace function for replacing a renderable in the datasource.

Improvements:

• context.set now returns the data that was set (for convenience).
• Added css-linting to the grunt build script.
• Added removeSpec argument to .removeAll.
• Prevent reflow when using .insert(id) to set a renderable which was already at that id.

Fixed:

• Updated global dist/famous-flex-global.js to work properly with browserify (IjzerenHein -> renamed to famousflex)
• Fixed background in TabBarLayout not correctly calculated when top/bottom margins are used.
• Fixed scrollend event not emitted when alwaysLayout is enabled.
• Fixed various linting & style errors/warnings.
• Fixed issue with renderables not animating according to removeSpec when removed from LayoutController.
• Fixed .ensureVisible function which always caused a big visual hickup.
• Fixed exception in .remove when a ViewSequence was used as datasource.
• Fixed .insert which did not always return the chainable this class.