Combine CCoinsViewCache's HaveCoins and const GetCoins into AccessCoins.

The efficient version of CCoinsViewCache::GetCoins only works for known-to-exist
cache entries, requiring a separate HaveCoins call beforehand. This is
inefficient as both perform a hashtable lookup.

Replace the non-mutable GetCoins with AccessCoins, which returns a potentially-NULL
pointer. This also decreases the overloading of GetCoins.

Also replace some copying (inefficient) GetCoins calls with equivalent AccessCoins,
decreasing the copying.
netbase: Use .data() instead of .c_str() on binary string

`.c_str()` is only guaranteed to return the data up to the first NUL
character.
Avoid repeated lookups in mapOrphanTransactions and mapOrphanTransactionsByPrev
Rename script.h/.cpp to scriptutils.h/.cpp (plus remove duplicated includes)
Move CScript class and dependencies to script/script
Separate script/interpreter
Separate script/standard
Separate CScriptCompressor
Separate script/sign
Merge pull request #4754

e088d65 Separate script/sign (jtimon)
9294a4b Separate CScriptCompressor (jtimon)
c4408a6 Separate script/standard (jtimon)
da03e6e Separate script/interpreter (jtimon)
cbd22a5 Move CScript class and dependencies to script/script (jtimon)
86dbeea Rename script.h/.cpp to scriptutils.h/.cpp (plus remove duplicated includes) (jtimon)

Rebased-by: Pieter Wuille
Merge pull request #4873

89d91f6 Avoid repeated lookups in mapOrphanTransactions and mapOrphanTransactionsByPrev (Wladimir J. van der Laan)
Remove some unnecessary c_strs() in logging and the GUI

Includes `core: remove unneeded c_str() / Qt: replace c_str() with Qt code`
by P. Kaufmann.
Merge pull request #4868

2c2cc5d Remove some unnecessary c_strs() in logging and the GUI (Philip Kaufmann)
f7d0a86 netbase: Use .data() instead of .c_str() on binary string (Wladimir J. van der Laan)
remove unneeded cast in rpcmisc.cpp
Merge pull request #4882

faadbe1 remove unneeded cast in rpcmisc.cpp (Philip Kaufmann)
Merge pull request #4822

629d75f Combine CCoinsViewCache's HaveCoins and const GetCoins into AccessCoins. (Pieter Wuille)