Read project configuration from .jshintrc file in project

In order to reuse the configuration for jshint checks outside
Eclipse, we read the config from .jshintrc file in the project
instead of storing it in the project properties.

The "Options" property page does not allow editing options and
globals anymore, the config file must be edited instead.

Fixes #28
Allow for comments in config files

JSHint permits comments in .jshintrc files. To be able to share
config files with JSHint, we have to filter out comments before
parsing as JSON.
Remove support for JSLint

As JSHint diverges from JSLint, better support for JSHint requires to
drop support for JSLint. Examples are reading configuration from
.jshintrc files and evaluating jshint error codes to distinguish
between errors and warnings.

Fixes #54