Add maki icons via bower

[Henni]

This PR only includes the PNG versions of the maki icons.

@v1r0x please review

[v1r0x]

@Henni Thanks! Now one has to run bower install before using this app?

[Henni]

@v1r0x no. I included the pngs in the commit. But bower allows us to simply upgrade the 3rd party dependencies like maki in the future. BTW: this is similar to how core handles it https://github.com/owncloud/core/tree/master/core/vendor

[v1r0x]

ok, great :+1: