ImageJ.c: add --info for setting INFO log level

This is similar to --debug, but for INFO instead of DEBUG level output.
It will be useful for command line tools that need the log level set to
INFO instead of the (recently changed) default of WARN.
ImageJ.c: use INFO log level for the updater CLI

Otherwise, many updater commands emit no output.

Fixes #9.
Merge pull request #12 from imagej/info-logging-for-cli

Default to INFO log level for CLI tools