Clean up Plugin UI

[ahankinson]

A few tidying things:

1. I think the "Test extension" shouldn't be deployed by default, so I would like to remove it from the release code (i.e., not copy the .plg file to the release)
2. Similarly, all the test runners shouldn't be copied into the release.
3. I've already fixed up the dialog that pops up, since the buttons were cutting off the text labels and it looked really messy.

To do this I will create a plgconfig.js and a plgconfig_release.js, with the latter obviously being used for release.

Sound OK?

[rettinghaus]

Sounds very reasonable.