Use `ltx` from node-xmpp-core

See https://github.com/node-xmpp/node-xmpp-client/issues/42
...and https://github.com/node-xmpp/node-xmpp-core/pull/39
Merge pull request #44 from Nighthawk14/master

Add possibility to set a custom wait time for bosh connections
Fix all references to ltx
Merge pull request #43 from node-xmpp/ltx

Use `ltx` from node-xmpp-core
Switch dependency versions
1.0.0-alpha1
Switch back version numbers
Add prebind functionnality to node-xmpp-client