deletion functionality for mass edition

fix #1349 (closed) and #1241 (closed) by adding deletion functionality to mass edition. It adds checkboxes for each field in the mass edit layout, which allows delete fields by just checking the checkbox without modifying the field contents.

layouts/v7/modules/Vtiger/partials/EditViewContents.tpl

@@ -46,6 +46,9 @@
{assign var=COUNTER value=$COUNTER+1}
{/if}
<td class="fieldLabel alignMiddle">
+										{if $MASS_EDITION_MODE}
+											<input class="inputElement" id="include_in_mass_edit_{$FIELD_MODEL->getFieldName()}" data-update-field="{$FIELD_MODEL->getFieldName()}" type="checkbox">&nbsp;
+										{/if}
{if $isReferenceField eq "reference"}
{if $refrenceListCount > 1}
{assign var="DISPLAYID" value=$FIELD_MODEL->get('fieldvalue')}