[Qt] fix RecentRequestsTableModel function ambiuguity

- fixes a compiler ambiguity error with ::createIndex() called in
  RecentRequestsTableModel::index()
- also add some Q_UNUSED() macros
Squashed 'src/leveldb/' changes from 936b461..e991315

e991315 Merge upstream LevelDB 1.15.
0cfb990 Release LevelDB 1.15
02ac9f1 Merge upstream LevelDB 1.14.
0b9a89f Release LevelDB 1.14

git-subtree-dir: src/leveldb
git-subtree-split: e991315d7fe4ca84a98902578106cbffa3dcccfd
Merge src/leveldb changes for LevelDB 1.15
add new RPC implementation file `rpcmisc.cpp`
Move `getinfo` from rpcnet to rpcmisc

`getinfo` is a general info method which shows information
from multiple sources, it doesn't belong in rpcnet.cpp or
any of the other current RPC implementation files.
Move `settxfee` from rpcblockchain to rpcwallet

`settxfee` only affects the wallet, not the block chain.
Move `nTransactionFee` from main.cpp to wallet.cpp

Transaction fee is only used by the wallet.
No need for it to be in main.cpp.
Move `validateaddress` from rpcwallet to rpcmisc

Enables it in --disable-wallet compiles.
Delimit wallet-using part using #ifdef ENABLE_WALLET.
Move `createmultisig` from rpcwallet to rpcmisc

Enables it in --disable-wallet compiles.
Move `verifymessage` from rpcwallet to rpcmisc

Enables it in --disable-wallet compiles.
Remove unused ThreadSafeHandleURI from ui_interface
Remove unused ThreadSafeAskFee from ui_interface

ThreadSafeAskFee is effectively unused. It is only called
when the fAskFee parameter on SendMoney or SendMoneyToDestination
is true, which never happens. Remove it.
qt: status WalletModel::Aborted is no longer used

Aborting transactions happens in the GUI now as it should,
not the backend.
Seperate out wallet options in help message

Seperate out the wallet options in HelpMessage, and
don't show them if compiled with --disable-wallet.

Also add documentation for `-disablewallet` option.
Fix typo in unit-tests.md
Merge pull request #3430 from ldenman/patch-1

Fix typo in unit-tests.md
Fix typos in spendfrom README
some more small re-branding changes (Bitcoin Core)
Merge pull request #3434

46469d0 some more small re-branding changes (Bitcoin Core) (Philip Kaufmann)
Merge pull request #3431

131c3db Fix typos in spendfrom README (Lake Denman)