[jinterface] add Eclipse projects and settings

For other IDEs, use these as reference. In short, the formatting
style is:

- indentation uses only spaces; each level is 4 positions
- no trailing whitespace
- mostly default Java style formatting (any difference is minor)

- always use {}
- use 'final' as much as possible
[jinterface] cleanup code according to new style
add OtpErlang and friends [beta]
set required Java version to 1.6