Rename "Open" to "Add/Open" in the inline editor

Per discussion with @Ben, from a users experence its better to call
this 'Add/Open' rather than 'Open'.

Change-Id: I8db0de50da0451fa4a95c6545172134c8094c597

polygerrit-ui/app/elements/edit/gr-edit-constants.html

@@ -22,7 +22,7 @@ limitations under the License.
 
     // Order corresponds to order in the UI.
     GrEditConstants.Actions = {
-      OPEN: {label: 'Open', id: 'open'},
+      OPEN: {label: 'Add/Open', id: 'open'},
       DELETE: {label: 'Delete', id: 'delete'},
       RENAME: {label: 'Rename', id: 'rename'},
       RESTORE: {label: 'Restore', id: 'restore'},

polygerrit-ui/app/elements/edit/gr-edit-controls/gr-edit-controls.html

@@ -89,12 +89,12 @@ limitations under the License.
           id="openDialog"
           class="invisible dialog"
           disabled$="[[!_isValidPath(_path)]]"
-          confirm-label="Open"
+          confirm-label="Confirm"
           confirm-on-enter
           on-confirm="_handleOpenConfirm"
           on-cancel="_handleDialogCancel">
         <div class="header" slot="header">
-          Open an existing or new file
+          Add a new file or open an existing file
         </div>
         <div class="main" slot="main">
           <gr-autocomplete