Naive impl of "selected" function in expression editor
Refactor: generic expression parse/construct
Set "selected" operator on drop multi-select
Fail to advanced editor on wrong number of args

This could happen if the user typed an expression like `selected(/data/things, 'thing1', 'thing2')` (which incidentally may not be a valid function call). Previously the third argument would have been silently discarded.
Do not use "selected" function on single-select

The Select mug extends the MSelect, and it inherited its defaultOperator. This fix overrides that default.
Merge pull request #189 from dimagi/104232-selected-function

Add "has selected value" operation to simple expression builder
Group all unknown reference errors
Show all error messages

...instead of only the last one in the list. Adjusted CSS to prevent a huge error message from flooding the screen and making it impossible to access the close button (x) on the error message.
Fix the group-move bug

References to group's children were not being updated. A new updatePaths() method was added because the updatePath() method clobbered the LogicManager's internal state while updating the first path:

setMugPropertyValue
    -> property-changed event
    -> LogicManager.updateReferences(mug, propertyPath)
    -> LogicManager.all items for mug are cleared,
      and new items added, but paths are now invalid so ref === ""
Fix bad english
Removed 'CodeMirror' syntax highlighter.
Fix mug type conversion bug

Checking the exception message is not portable across different browsers (failed on Chrome, worked on Firefox).
Remove broken code

Note sure why this line was here; there is no `input` in scope.
Merge pull request #203 from dimagi/fix-broken-code

Remove broken code
Merge pull request #202 from dimagi/108638-type-change-fix

Fix mug type conversion bug
Merge pull request #199 from dimagi/48588-group-move-bug

Fix group move bug
Merge pull request #200 from msienkiewicz/75446-case

Removed 'CodeMirror' syntax highlighter.
updating xpath ref
Revert "Removed 'CodeMirror' syntax highlighter."

This reverts commit ac61be31429d2e90f73e7d4ce4f6ca837f33e1c3.
restore ctrl-f in source xml editor