#666 Support multiple lines for formulas in theory editor

[Nicolas Beauger]

In the theory editor, the formulas are entered in a single line.
For instance, the 'Direct definition' of an operator.
It is often more comfortable to put these formulas on several lines.

In org.eventb.theory.ui plug-in, extension "org.eventb.ui.editorItems", setting
textAttribute id="org.eventb.theory.ui.formula" with style="multi" instead of "single" would do it.

[Nicolas Beauger]

Fixed by commit 15642.