Use fpm --list to generate targets

[everythingfunctional]

Using the --list option should allow us to determine what targets are actually available and include them as available targets in the plugin, instead of having users specify the target they'd like to use in the Settings.

Relevant commands would be:

• fpm run --list
• fpm run --example --list
• fpm test --list

If none are listed for a given command, don't provide any targets. If only one is listed, provide only a single target for that command without any additional description. If multiple are listed, provide an all target, as well as each individual one listed.

This has a (probably negative) side-effect that fpm (re)builds the project when these commands are executed. Maybe this should wait until fpm can be modified to not (re)build with these commands?