Making relevant functions/variables protected

Any functions/variables that could've been made protected have been made so.  However, there are quite a few functions/variables that are still under the public underscore protection that we may want to look at.  This includes:
timeScale.tickInterval API added

- [x] abstractComponent._element
- [x] abstractComponent._content
- [x] abstractComponent._backgroundContainer
- [x] abstractComponent._foregroundContainer
- [x] abstractComponent._anchor
- [x] abstractComponent._requestedSpace
- [x] abstractComponent._computeLayout
- [x] abstractComponent._isFixedWidth
- [x] abstractComponent._isFixedHeight
- [x] abstractComponent._doRender
- [x] abstractComponent._invalidateLayout
- [x] abstractComponent._parent
- [x] abstractComponent._render
- [x] dataset_getExtent
- [x] abstractDrawer._renderArea
- [x] absractDrawer._enterData
- [x] abstractDrawer._drawStep
- [x] elementDrawer._getDrawSelection
- [x] abstractInteraction._anchor
- [x] abstractScale._typeCoercer
- [x] abstractScale._autoDomainIfAutomaticMode
- [x] abstractScale._updateExtent
- [x] abstractScale._removeExtent
- [x] timeScale._tickInterval
- [x] dragBoxInteraction._CAN_RESIZE_X
- [x] dragBoxInteraction._CAN_RESIZE_Y
- [x] hoverable._hoverOverComponent
- [x] hoverable._hoverOutComponent
- [x] hoverable._doHover
- [x] plottableObject._plottableID
- [x] abstractInteraction._hitBox
- [x] abstractInteraction._componentToListenTo
- [x] quantitativeScale._defaultExtent
- [x] quantitativeScale._niceDomain
- [x] quantitativeScale._userSetDomainer