Linkstate refactor (#609)

* Linkingstate Refactor, and displaying link info in rightpanel

Big refactor to LinkingState
    Collects descriptive/user-facing labels into FilterState
    Unifies/cleans up some logic
    Adds LinkTypeDescription, a string enum which can be used
    to easily switch/case between various cases of linking, and
    codifies the logic in one place (currently only used for linkInfo)

Adds Link info to creator panel, near SelectBy dropdown

Bugfix: Disables linking from Attachment columns
Bugfix/Behavior change: changed linking with empty RefLists to better
match behavior of refs.
    for context: Linking by a blank Ref filters to show records with a
    blank value for that Ref. Previously this didn't work with RefLists. 
    Linking from a blank refList would show no records 
    (except in some cases involving summary tables)
    Fixed this so that linking by a blank val consistently means "show
    all records where the corresponding col is blank"

test/nbrowser/RightPanel.ts

@@ -245,7 +245,7 @@ describe('RightPanel', function() {
 
     // check that selector-of is present and that all selected section are listed
     assert.equal(await driver.find('.test-selector-for').isPresent(), true);
-    assert.deepEqual(await driver.findAll('.test-selector-for-entry', (e) => e.getText()), [
+    assert.deepEqual(await driver.findAll('.test-selector-for-entry', (e) => e.getText().then(s => s.split('\n')[0])), [
       "CITY",
       "COUNTRYLANGUAGE",
       "COUNTRY Card List",