[Icons] [MonoDevelop.Ide] F# icons implemented:

* `md-exception` mapped to `element-exception-light-16.png'
* `md-fs-field` mapped to `element-fs-field-light-16.png`
* `md-module` mapped to `element-module-light-16.png`
* `md-other-declaration` mapped to `element-other-declaration-light-16.png`
* `md-type` mapped to `element-type-light-16.png`
* `md-script-file-icon` mapped to `file-script-light-16.png` and `file-script-light-32.png`

See https://github.com/xamarin/icons/commit/3692ed1f7ff41513628eae43402d2e562298247f

Signed-off-by: Vaclav Vancura <vaclav@vancura.org>