Tweak javadoc
ScriptFinder: tweak name of script icon constant
Standardize text referring to scripting languages
DefaultScriptService: remove obsolete override

The getPluginService() method is actually implemented in the
AbstractPTService superclass, and the override here is both
needless and misleading.
DefaultScriptService: fix method order
Improve some variable and method names
DefaultScriptService: rename method for simplicity

Also add some quick comments to the method body.
AbstractModuleInfo: remove repeated javadoc
Change how scripts are discovered and managed

This is the start of a Grand Unification of the scripting framework, but
not yet complete. Previously, discovered scripts were Command wrappers
added to the CommandService using the ScriptPlugin adapter. However, a
script really is *not* a Command, because a Command is a Plugin, and
scripts are not Plugins (a Plugin is a Java class annotated with
@Plugin; scripts are not Java classes).

A script can, however, be expressed a Module. So we define a new type of
Module called ScriptModule to accomplish this, with a corresponding new
type of ModuleInfo called ScriptInfo for storing script-specific
metadata (in particular, the path to the script on disk, if any).
Add a new command for executing scripts

It is nice to have a Command that takes as input a file containing a
script to execute, and then executes said script (producing no formal
outputs). The ScriptPlugin was previously such a command, but it did
lean on ScriptService#eval, probably because that method did not yet
exist when it was first written.

The ScriptPlugin also doubled as a command wrapper for the discovered
scripts themselves, which was a rather unfortunate and ultimately
inflexible way of doing things (rather, we want each script to have
properly typed inputs and outputs to the extent possible).

So this change removes the old ScriptPlugin (nothing is using it anymore
anyway) and adds a simple RunScript command into ij-commands that
serves the former purpose, while abandoning the script wrapping aspect.