Install button available when no plugins selected

[Donovan Keith]

To Reproduce

1. Open CV Toolbox
2. Click on the "Install" button
3. BUG: CV attempts an install of nothing and spit out an error.

Expected behavior

A) A dialog pops up saying "Please check the boxes next to the tool(s) you'd like to install and try again." and keeps the user on the tools list page. B) "Install" button is grayed out - probably the simplest, but it doesn't educate the user on what they're supposed to do to gain access to the install button. C) Install whichever tool is currently "selected" (e.g. orange). - This is the most intuitive for users, but leads to logic/consistency issues when a user has checked multiple plugins but now has a different on selected.

My vote is for option A.

When trying to report this bug, I ran into another which I'll post about soon.