Added png compression task

```
Running "pngmin" task
>> Compressed 8 files
>> Uncompressed size: 186kb, Compressed size: 25.76kb, Savings: 86.15%
```
Calendar: Replaced all calendar icons with glyphicons
Merge pull request #3781 from pjackson28/switchcalendaricontoglyphicon

Calendar: Replaced all calendar icons with glyphicons
Tabs: Aligned with WAI-ARIA tabpanel design pattern (fixes #3738)
Merge pull request #3782 from pjackson28/tabskeyboardsupport

Tabs: Aligned with WAI-ARIA tabpanel design pattern (fixes #3738)
Demos: Move non-plug-in pages to site folder
Site: Order i18n strings
Site: Add i18n friendly footer

- Falls back to English for the Web Standards site for non-French pages
- Added additional translations to i18n JSON files
Tables: Replaced image icons with glyphicons
Site: Add i18n friendly sitemenu
Merge pull request #3784 from pjackson28/switchtablestoglyphicons

Tables: Replaced image icons with glyphicons
Calendar: Fixed arrow display glitches and undefined data errors
Merge pull request #3783 from nschonni/v4-demo-organization

Demos: Move non-plug-in pages to site folder
Site: Add i18n friendly fullmenu
Merge pull request #3786 from pjackson28/fixeventscalendar

Calendar: Fixed arrow display glitches and undefined data errors
Share: Fixed share widget link inner padding issue (fixes #3779)
Merge pull request #3787 from nschonni/v4-site-i18n-cleaning

V4 site i18n improvements
Merge pull request #3788 from pjackson28/fixsharewidget

Share: Fixed share widget link inner padding issue (fixes #3779)
Merge pull request #3679 from LaurentGoderre/v4-optimize-images

Added png compression task