MAGETWO-31195: Image compression and sizing

- Changed part images from .gif to .png
- Additionaly minified images
- Cleaned unused .gif

Author: Bogdan Plieshka

app/code/Magento/Backend/Block/System/Design/Edit/Tab/General.php

@@ -97,7 +97,7 @@ protected function _prepareForm()
                 'label' => __('Date From'),
                 'title' => __('Date From'),
                 'name' => 'date_from',
-                'image' => $this->getViewFileUrl('images/grid-cal.gif'),
+                'image' => $this->getViewFileUrl('images/grid-cal.png'),
                 'date_format' => $dateFormat
                 //'required' => true
             ]
@@ -109,7 +109,7 @@ protected function _prepareForm()
                 'label' => __('Date To'),
                 'title' => __('Date To'),
                 'name' => 'date_to',
-                'image' => $this->getViewFileUrl('images/grid-cal.gif'),
+                'image' => $this->getViewFileUrl('images/grid-cal.png'),
                 'date_format' => $dateFormat
                 //'required' => true
             ]

app/code/Magento/Backend/Block/Widget/Form.php

@@ -226,7 +226,7 @@ protected function _applyTypeSpecificConfig($inputType, $element, \Magento\Eav\M
                 $element->setCanBeEmpty(true);
                 break;
             case 'date':
-                $element->setImage($this->getViewFileUrl('images/grid-cal.gif'));
+                $element->setImage($this->getViewFileUrl('images/grid-cal.png'));
                 $element->setDateFormat($this->_localeDate->getDateFormatWithLongYear());
                 break;
             case 'multiline':

app/code/Magento/Backend/Block/Widget/Grid/Column/Filter/Date.php

@@ -96,7 +96,7 @@ public function getHtml()
             '",
                     buttonImage: "' .
             $this->getViewFileUrl(
-                'images/grid-cal.gif'
+                'images/grid-cal.png'
             ) . '",
                         buttonText: "' . $this->escapeHtml(__('Date selector')) .
             '",

app/code/Magento/Backend/Block/Widget/Grid/Column/Filter/Datetime.php

@@ -136,7 +136,7 @@ public function getHtml()
                         dateFormat: "' . $format . '",
                         timeFormat: "' . $timeFormat . '",
                         showsTime: ' . ($this->getColumn()->getFilterTime() ? 'true' : 'false') . ',
-                        buttonImage: "' . $this->getViewFileUrl('images/grid-cal.gif') . '",
+                        buttonImage: "' . $this->getViewFileUrl('images/grid-cal.png') . '",
                         buttonText: "' . $this->escapeHtml(__('Date selector')) . '",
                         from: {
                             id: "' . $htmlId . '_from"