Updated default title theme

Applied the theme properly to chart titles
Added titlePadding variable
Merge pull request #188 from niksoper/develop

Updated default title theme
Factor out axis strategies

Uses separate strategies for different axis types.
Pulls out the domain, findMin, findMax, and findOrdinal methods into the
new strategy.
Introduce basic tickFrequency calculation

Adds the tickFrequency method to the Axis, and hooks it in to tickValues
for linear scales.

For now, date and category scales use the same tick values they
previously used.
Introduce tickValues to axis

also allows axis tickFrequency to be set by the user
Added filterChanged method

Acts as an event that can be used to notify the client that filtering has changed in some way on a ChartGroup.
Reduced opacity of 'notselected' points

This makes it clearer which bubble has been highlighted on a bubble chart.
Increase/Decrease ticks by step

Implements the increase/decreaseTickStep method, to generate the next or
previous tick from the current one, with different implementations for
ordinal, linear and date axes.
Implement Auto-frequency for dates

Adds the initial, increase and decrease methods for tick frequency.
We have a preset list of frequencies for dates, from 1s to 100yr.
Introduce initialTickValue to axis

For this to work for a date axis, a date round function has been
introduced.
Merge pull request #189 from niksoper/develop

ChartGroup filterChanged
Update axis draw to use auto-tick values
Using one tooltip per chart rather than per series
Updated comment after adding initializeTooltip to Chart.
Typo: offest => offset
Updated comment: Series => chart.
Allowing series to have different tooltip offsets

The tooltip offset needed to be set on mouseover rather than when the
series is drawn. This means that the positionTooltip function is not
needed.
Removed tests for Series.initializeTooltip
Update axis calculation for interactive axes