Add long overdue Javadoc for the TextEditor class

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
WIP: depend on SNAPSHOT version of scripting-java

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
WIP: Add Auto-Import feature

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>