[Fixed Position] Add ability to work in pixel space

Fix code style issues per Victor's review

Add toggle to work in pixel space or grid space, per the issue description.
Each element stores a boolean property that determines whether or not it
snaps to grid space or pixel space. Coordinates are converted between spaces
on toggle, preserving the size of the element in pixels.

To complete: change UI element for toggle to a checkbox.

platform/features/layout/res/templates/elements/line.html

@@ -19,12 +19,12 @@
  this source code distribution or the Licensing information page available
  at runtime from the About dialog for additional information.
 -->
-<svg ng-attr-width="{{parameters.gridSize[0] * ngModel.width()}}"
-     ng-attr-height="{{parameters.gridSize[1] * ngModel.height()}}">
-    <line ng-attr-x1="{{parameters.gridSize[0] * ngModel.x1() + 1}}"
-          ng-attr-y1="{{parameters.gridSize[1] * ngModel.y1() + 1}}"
-          ng-attr-x2="{{parameters.gridSize[0] * ngModel.x2() + 1}}"
-          ng-attr-y2="{{parameters.gridSize[1] * ngModel.y2() + 1}}"
+<svg ng-attr-width="{{ngModel.getGridSize()[0] * ngModel.width()}}"
+     ng-attr-height="{{ngModel.getGridSize()[1] * ngModel.height()}}">
+    <line ng-attr-x1="{{ngModel.getGridSize()[0] * ngModel.x1() + 1}}"
+          ng-attr-y1="{{ngModel.getGridSize()[1] * ngModel.y1() + 1}}"
+          ng-attr-x2="{{ngModel.getGridSize()[0] * ngModel.x2() + 1}}"
+          ng-attr-y2="{{ngModel.getGridSize()[1] * ngModel.y2() + 1}}"
           ng-attr-stroke="{{ngModel.stroke()}}"
           stroke-width="2">
     </line>