Remove warnings from Travis and devtools::test() checks

[connectedblue]

This PR proposes some updates to the existing code base to prevent warnings thrown by some test tools. This was discussed in #186.

The warnings fixed by this are:

• those thrown when devtools::test() is run in the ProjectTemplate directory
• when examining the travis console screen warnings were shown about the binding of the config variable in .remove.sticky.variables() function.

No user functionality is changed in this PR, it simply cleans up some underlying test cases to improve the regression suite.

[connectedblue]

Hi @KentonWhite Could you review and merge this PR if you're happy with it?

It touches some files which I'll need to modify to address the bug in #192 so I'd rather develop off the master with the cleaned up tests.

[KentonWhite]

Merged. Thanks!