Add in the recalculated index to the wrapped elements

We want to be able to find out what the calculated
index is for amino acid elements.
Change display of conservation

For conserved areas, just use the alignment string and use
a traditional dark == conserved scheme.
Add in font-size options for callouts

We need the ability to edit the font size on callouts
from the options hash
Fix for rendering speed

We can skip over rendering of hidden elements, as well as
avoiding the invalidation of style caused by changing
the cursor.
Optimisation fix for redrawing axis.

After playing around in the Speed Tracer, it became evident
that there were a number of blocking blocks of code that were
slowing things down. We can make some quick and easy optimisations
to beat this.
Avoid recalculating layout for the container node

We can use a cached width that is only updated on window resize.
This avoid the approx. 50ms overhead that we get from recalculating
the layout each time we calculate the right-most visible residue
or the minimum zoom.