Manage network screen

[Tbaut]

This page should be available from the top level of the app.
It should:

• show the default networks available (Ethereum, Kovan, Kusama...) without delete button
• show the added networks with the ability to delete them (no edit for now)
• show the genesis hash (0xe53787...ad87689) or chaid id for Etereum based network
• show a "add network" button similar to the Scan button (bringing to the scanner)