[optimization] Avoid to load whole material design font

[sbernard31]

Issue

Currently we load the whole material design font, this is not so good 😬 ...

This is arround 350 Ko and 1.1Mo downloaded (depending format used by the browser) which is mainly not used.

This PR aims to use @mdi/js which supports webpack tree shaking to only get used icons.
See : https://stackoverflow.com/questions/57552261/vuetifyjs-adding-only-used-icons-to-build

Results

This PR removes warnings below raised by webpack (#1239):

asset size limit: The following asset(s) exceed the recommended size limit (244 KiB).
This can impact web performance.
Assets: 
  fonts/materialdesignicons-webfont.aaf5968f.eot (1.11 MiB)
  fonts/materialdesignicons-webfont.ad0f7b3f.woff2 (358 KiB)
  fonts/materialdesignicons-webfont.f5b84261.ttf (1.11 MiB)
  fonts/materialdesignicons-webfont.fabeafb8.woff (516 KiB)

Following Firefox devTools, among of data to load to open main web page is reduced about 600 ko :

• from 1.67 Mo to 1.05 Mo for leshan-server-demo
• from 1.62 Mo to 0.99 Mo for leshan-bsserver-demo

Both jars also reduce about ~600Ko :

• from 15.1 Mo to 14.5 Mo for leshan-server-demo
• from 13.2 Mo to 12,8 Mo for leshan-bsserver-demo

This also increases the lighthouse(#1240) score from ~10 point. (But score seems to not be exactly the same each runs...)
E.g. for server-demo (tested locally), before :

Then after :