Easy way of browsing and selecting from available ops

As things stand, it is a little challenging to quickly see the available/relevant ops. We have the `OpService#help(String)` command, but that gives you all signatures for operations of that name. There is no instant gratification "auto-complete" style thing available in Eclipse, since OPS works its magic at runtime rather than compile time. It would be great to remedy that situation somehow.

One option would be a UI allowing for the browsing and selection of ops, for the purposes of search, filtering and execution. This would essentially be a [Command Finder](http://imagej.net/Command_Finder) for OPS. Since an `Op` is already a command, the IJ2 Command Finder actually already displays all ops, but not the list of input parameters nor descriptions where available. So the UI proposed here would be slightly different than just another Command Finder.

A second possibility would be an Eclipse plugin for OPS that gives you code completion from within the IDE. This would be incredibly slick and useful, and is the option I am leaning toward at the moment.