Improve fonts loading

[m4dz]

In some apps, text may flicker due to the loading of our webfonts. This is mainly due to network latencies which causes a delay and a repaint of the viewport when fonts are finally available.There's 2 solutions fir this issue:

1. Stop using a non-websafe font for the main font and let the UA choices
2. Lazy-load the fonts using Fonts Events as it's the currenlty recommended way.

The second solution is more smart bu needs to do it properly on all our webapps (not only in the proxy).

[frankrousseau]

@m4dz Can you recommend a websafe font?

[m4dz]

Our main issue is due to source sans pro used for labor. Maybe we can make de test of clever loading on the proxy and replicate the method in other apps. Or just leav it and set labor font to sans-serif to let user OS choose the best sans-serif font (which may result to a better look'n feel on OSes like iOS or OS X).

@kelukelu any thoughts?