Transparency slider values have different number of digits after the decimal, causing little jumps

This issue has been migrated from mozilla/webmaker-android#1793.

It was originally written by flukeout on Mon May 11 2015 and had the following description:

When you adjust the transparency of an Image Element, the value shifts around a bit when you switch between values like .81 and .8

We can solve this by left-aligning the value or by always having a two digit value, .80 instead of .8 (with special exceptions for 0 and 1).

**@**vazquez What do you think?

On Mon May 11 2015, vazquez commented:

I would propose left aligning the values.