* params: add IsIstanbul to config + rules

IstanbulBlock, used to determine if the config IsIstanbul, is currently
left nil until an actual block is chosen.

* params, core/vm: implement EIP-1108

Old gas costs for elliptic curve operations are given the PreIstanbul
prefix, while current gas costs retain the unprefixed names. The actual
precompile implementations are the same, so they are factored out into
common functions that are called by the pre-Istanbul and current
precompile structs. Finally, an Istanbul precompile list is added that
references the new precompile structs, which in turn reference the new
gas costs.

* params: fix fork ordering, add missing chain compatibility check