Icon extension for package manager and manifest fix

Icon extension for package manager and manifest fix

[Issue#]       LINUXWRT-804 / WGL-428
[Bug]          Hardcoded .png extension
[Cause]        N/A
[Solution]     Use extension of used icon
[SCMRequest]   This requries wrt-commons change: https://review.tizendev.org/gerrit/86777
[Verification] Install widget from https://bugs.tizendev.org/jira/browse/WGL-428.
Manifest file in /opt/share/packages/J7tHY89x22.xml should contain icon with .svg extension
(<icon>J7tHY89x22.Y2y1.svg</icon>).

Change-Id: Ifef3f38e1566b92817f62aa01c1ac73bc073d71b