util, model, search_controllers: Add plugin hook points

Add plugin hook points to be used in plugin cqp_between_tokens.

app/scripts/model.js:
- BaseProxy.expandCQP: Let plugins filter the expanded CQP.

app/scripts/search_controllers.js
- ExtendedSearch: Let plugins filter the extended search CQP expression
  and act when corpus selection is changed.

app/scripts/util.js
- CorpusListing.constructor, .select: Let plugins act on CorpusListing
  after constructing it and when selecting corpora.

app/scripts/model.js

@@ -34,12 +34,16 @@ class BaseProxy {
     }
 
     expandCQP(cqp) {
+        let result
         try {
-            return CQP.expandOperators(cqp)
+            result = CQP.expandOperators(cqp)
         } catch (e) {
             c.warn("CQP expansion failed", cqp, e)
-            return cqp
+            result = cqp
         }
+        // Let plugins filter the expanded CQP
+        result = plugins.callFilters("filterExpandedCQP", result)
+        return result
     }
 
     makeRequest() {

app/scripts/search_controllers.js

@@ -455,6 +455,8 @@ korpApp.controller("ExtendedSearch", function ($scope, $location, $rootScope, se
         if ($rootScope.globalFilter) {
             val2 = CQP.stringify(CQP.mergeCqpExprs(CQP.parse(val2 || "[]"), $rootScope.globalFilter))
         }
+        // Let plugins filter the extended search CQP expression
+        val2 = plugins.callFilters("filterExtendedCQP", val2)
         $rootScope.extendedCQP = val2
     }
 
@@ -488,6 +490,8 @@ korpApp.controller("ExtendedSearch", function ($scope, $location, $rootScope, se
     return s.$on("corpuschooserchange", function () {
         s.withins = s.getWithins()
         s.within = s.withins[0] && s.withins[0].value
+        // Let plugins act when corpus selection is changed
+        plugins.callActions("onCorpusChooserChange")
     })
 })
 

app/scripts/util.js

@@ -31,6 +31,8 @@ window.CorpusListing = class CorpusListing {
             "getStructAttrsIntersection",
             "getStructAttrs",
         ])
+        // Let plugins act on CorpusListing after constructing it
+        plugins.callActions("onCorpusListingConstructed", this)
     }
 
     get(key) {
@@ -63,6 +65,9 @@ window.CorpusListing = class CorpusListing {
 
     select(idArray) {
         this.selected = _.values(_.pick.apply(this, [this.struct].concat(idArray)))
+        // Let plugins act on CorpusListing when selecting the corpora
+        // listed in idArray
+        plugins.callActions("onCorpusListingSelect", this, idArray)
     }
 
     mapSelectedCorpora(f) {