This change adjusts BindingManager.resolveConflicts() to check the
potentially conflicting bindings for disabled handlers. If at least one
of the bindings has a disabled command handler, no key binding conflict
is reported.

This helps e.g. with the Ctrl+Shift+T key bindings reported when JDT and
LSP4E are both installed in Eclipse. No key binding conflict is reported
when no editor with a language server is open, since the LSP4E binding
has an enabled handler only then.

Fixes: #1507
Signed-off-by: Simeon Andreev <simeon.danailov.andreev@gmail.com>