POM: add dependencies to jar and add main class to manifest
fix index by position calculation

It's not completely fixed. For marking stuff it would be nice to use either
byte depending on where the user drags to. This would require
differentiating between positions on and positions between bytes.
add HexSelectionListener
move hover and selection management to scrollable panel

Hover and selection display are actually kinda specific use cases and
therefore don't belong in the HexPanel which should only have very
generic capabilities. Along those lines, I'll probably move the ability
to scroll some time too.