Support specifying font awesome icons for apps

[ericfranz]

1. OodApp#fa_icon can delegate to manifest#fa_icon
2. manifests have a new field in yaml: fa_icon: gear
3. default value in manifest is gear
4. the logic of the dashboard will be that if icon.png is not present, use fa_icon instead

[ericfranz]

This will let us use the manifest to specify all the icons for all the sys apps that we currently use.

[ericfranz]

• another alternative is in manifest instead of fa_icon: gear we do icon: fa-gear - could open up other options in future

[nickjer]

Not a fan of adding fa_icon to manifest. I prefer your latter suggestion a "bit" more.

Unfortunately I can't think of a better option right now.

[ericfranz]

okay, we will do:

• manifest: icon: fa-gear
• default is fa-gear
• for now, assume only valid value for icon in manifest is a font-awesome class name - but later we can support other values - so OodApp#fa_icon can still be added (and we can change this later as necessary)

[nickjer]

Maybe something like:

icon: file://./path/to/image.png
icon: fa://gear
icon: http://my.cdn.com/img.png

[ericfranz]

icon: fa://gear

and only support fa://gear for now. If icon.png is in root, use that instead.