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]    Missing an API that can retrieve file extension.
[Solution] Make use the file extension of used icon

[SCMRequest] Depends upon https://review.tizendev.org/gerrit/86777
[Verification]
   1. Install widget from https://bugs.tizendev.org/jira/browse/WGL-428.
   2. Manifest file in /opt/share/packages/J7tHY89x22.xml should contain icon with .svg extension
      (<icon>J7tHY89x22.Y2y1.svg</icon>).

Change-Id: I06ccc45566afe8b49f39515e192ce58a1c1cac86