Add the ability to change to label text

This allows changing the prompt label, that until now was hardcoded to
be only to, to be edited to any value. Changing the label will incur a
small performance penalty, as to ensure layout is appropriate, data is
completely reloaded at this point. This closes #4.
Fix layout issue causing the token field to be too tall

Because reloadData was being called before layoutScrollView, the scroll
view had a 0 width when attempting to calculate an initial height. This
meant that the first time the height was recalculated after being
displayed it would resize to the initially miscalculated 2 lines of
tokens height. Since there was no need for this, the input field stayed
on the first line, and there was a much larger section for the token
field than necessary. By skipping the setter call and just addressing
the label text directly, we avoid kicking off a data reload and its
associated layout run. Later changes (after rendering) will still cause
a data reload, preventing the client from having to manually reload any
time they change the prompt text.
fix style and minor bugs
Merge pull request #14 from brandnetworks/customizable-to-label

Add the ability to change to label text