Refactor FontAwsome plugin

[MysticJay]

1. The plugin uses an old version of FontAwsome
2. change: from using a Font to SVGs

Related: IITC-CE/ingress-intel-total-conversion#236

prosed DEV steps:

1. replace font based to SVG based using lastest FA-Icons

This will overcome the need to hold a whole font in memory. Icons will only be fetched on need.

2. design SVG based IITC icons to replace FA.
   Pro: we become independent from external resources

Contra: an own set of icons is limited to those already designed. Plugins that need a new icon would need to request extending the set or create an own icon.

3. submit as proposal to IITC.

[MysticJay]

As SVG-based Icons are to be preferred, we have to decide where to store them.

Goals:
have a UI that allows to use ICON-Buttons.
allow to use same icons by plugins.
Provide many different Icons for use with IITC and 3rd party plugins.

1. FontAwesome (FA) vs. selfdesigned set of ICONs
   Unless we have a developer who is willing to design a free to use set of ICONs for now and the future FontAwesome is a good choice.

2. Complete set vs. selected big set vs. minimum set
   based on FA we can integrate the complete set of icons (105 kB) or strip a number of icons that are not really likely to be used in IITC. Selecting these ICONs is technically easy, but requires a maintainer who will add new ICONs when requested. Providing only the ICONs used by IITC and the "official" plugins would not really serve the goals to get a common UI.

3. inline, own storage e.g. on IITC.APP, public storage
   This can not really be split from point 2, as the size matters a lot. While a public or self hosted external icon set would allow to access a lot of icons for different plugins it requires to get them form the WEB on each restart. Concerns: additional traffic, addressing a 3rd party site.