Stabilise annotation connector rendering in FF

Firefox makes the connector line and associated note wrapper float around
when the cursor is nearby if the top value is not fixed.

Fixes issue #49
Merge pull request #577 from peitschie/annotation-connector

Stabilise annotation connector rendering in FF
Consistently name Node.js like that
Add support for finding the Node.js executable on Debian
Merge pull request #585 from kossebau/supportDebiansNodejsExec

Support debian's nodejs exec
Add target webodf.js.zip-target
Change suffix of product targets to "-product"
Add special target "CI" for the CI