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.
Ignore develop branch artifacts
Display warning on drop circular reference

...in Display Condition or Calculate Condition.
Refactor/more descriptive warning message
Check mug absolute path as well as "."
Merge pull request #195 from dimagi/85054-warn-on-circ-ref

Display warning on drop circular reference in Display Condition or Calculate Condition
Roll back absolute path check

- It was broken (should have used that.form...)
- There's no way to drag/drop an absolute path anyway.
Merge pull request #196 from dimagi/85054-warn-on-circ-ref

Roll back absolute path check
Merge branch 'master' into develop

Conflicts:
	.gitignore
Fix .gitignore
fix placement of Show Simple (or Advanced) Mode buttons
Merge pull request #198 from dimagi/fix-buttons

fix placement of Show Simple (or Advanced) Mode buttons
Merge pull request #189 from dimagi/104232-selected-function

Add "has selected value" operation to simple expression builder
Merge branch 'master' into develop

Conflicts:
	src/js/ui.js
Generate vellum.min.js
track clicks on Edit buttons in Logic