Rename Toolbox to Tools

The name "Toolbox" is strangely anachronistic. Other functions in the
sidebar such as languages and navigation use very simple, functional
names.

Most translations already use a single word with meaning equivalent to
simply "Tools"; several use literal translations of "Box of tools",
which tends to look rather awkward.

Bug: 54910
Change-Id: I9ba287ec6426632847fe7d3a0d71948838496317
Merge "Rename Toolbox to Tools"