adjust fees per asset

[brenzi]

only roughly. no price oracles used yet

also fixes bogus ETH location transformation from #1710

tests

tester IncogniteeAHP account starts with 

L1: 0.003 ETH
shield 0.001 ETH
L1: 0.002 ETH
L2: 0.000998248686514887 ETH
send 0.0001 ETH to tester. received
L2: 0.000898248686514887
(fees were charged in DOT)
unshield 0.0005
L1: 0.0025 ETH
L2: 0.000398248686514887

Now testing if fees charged in ETH
send 0.0002 ETH to account without any DOT or other assets (tester2 local)
bal 0.0002
send 0.0001 back
bal 0.000094450000000000
fee 0.00000555 ETH