Refactored the abi package parsing and type handling. Relying mostly on
package reflect as opposed to most of our own type reflection. Our own
type reflection is still used however for cases such as Bytes and
FixedBytes (abi: bytes•).

This also inclused several fixes for slice handling of arbitrary and
fixed size for all supported types.

This also further removes implicit type casting such as assigning,
for example `[2]T{} = []T{1}` will fail, however `[2]T{} == []T{1, 2}`
(notice assigning *slice* to fixed size *array*). Assigning arrays to
slices will always succeed if they are of the same element type.

Incidentally also fixes #2379

rpc: remove NotifierContextKey

rpc: move web3.js extensions to internal/web3ext

Context keys must have a unique type in order to prevent
any unintented clashes. The code used int(1) as key.

Fix it by implementing the pattern recommended by package context.

accounts/abi/bind/backends: estimate needed gas, not used

all: fix go vet warnings

whisper: deflake Test*MessageExpiration

These tests have become a common annoyance on CI. Fix them by allowing
messages with expiration == now into the cache and delaying the check
for expired message handling slightly.

Lazy "I'll just put return here instead of fixing the test" found by go vet.

logging.printf triggered a format string warning. Silence it
by renaming the function.

This fixes a few uses of unkeyed Body literals which go vet was
complaining about.

all: update license information

cmd/utils: strip excessive whitespace from api command line arguments

eth: fix single transaction tracing (run prev mutations)

eth: add chaindbProperty to debug API (+ console fixes)

This makes web3 internals like _requestManager invisible.

accounts: disable filesystem notifications on iOS

jsre: print BigNumber objects with custom constructor as number

cmd/utils: fix accounts merge error on console unlock

accounts: cache key addresses