Introduce _module.selectable flag for trace modules [1852]

- Reason: code for checking if a trace supports selection was duplicated
  across the code base.

Author: rmoestl

src/components/modebar/manage.js

@@ -193,7 +193,7 @@ function isSelectable(fullData) {
 
         var trace = fullData[i];
 
-        if(!trace._module || !trace._module.getPointsIn || !trace._module.toggleSelected) continue;
+        if(!trace._module || !trace._module.selectable) continue;
 
         if(Registry.traceIs(trace, 'scatter-like')) {
             if(scatterSubTypes.hasMarkers(trace) || scatterSubTypes.hasText(trace)) {

src/plots/cartesian/select.js

@@ -462,8 +462,7 @@ function determineSearchTraces(gd, xAxes, yAxes) {
         cd = gd.calcdata[i];
         trace = cd[0].trace;
 
-        if(trace.visible !== true || !trace._module ||
-          !trace._module.toggleSelected || !trace._module.getPointsIn) continue;
+        if(trace.visible !== true || !trace._module || !trace._module.selectable) continue;
 
         // TODO is dragOptions.subplot is ever set? If not, delete.
         // if(dragOptions.subplot) {

src/plots/plots.js

@@ -1171,7 +1171,7 @@ plots.supplyTraceDefaults = function(traceIn, traceOut, colorIndex, layout, trac
             traceOut.visible = !!traceOut.visible;
         }
 
-        if(_module && _module.getPointsIn && _module.toggleSelected) {
+        if(_module && _module.selectable) {
             coerce('selectedpoints');
         }
 

src/registry.js

@@ -241,6 +241,8 @@ function registerTraceModule(_module) {
         exports.allCategories[categoriesIn[i]] = true;
     }
 
+    _module.selectable = _module.getPointsIn && _module.toggleSelected;
+
     exports.modules[thisType] = {
         _module: _module,
         categories: categoryObj