CMake: add OpenSSL version check

On OSX the version check helps to identify if the system OpenSSL
(which is old) is found instead of Homebrew's OpenSSL.
Before, the compilation failed while now we fail while executing
CMake with a much more readable error message.
Merge pull request #284 from toxeus/openSSLversion

CMake: add OpenSSL version check
OTCryptoOpenSSL: move functions into caller
OTCryptoOpenSSL: fix signature of callback definition
Merge pull request #285 from toxeus/OTCryptoOpenSSLCleanup

OTCryptoOpenSSL: cleanup declarations
Made OTContract::GetIdentifier(OTString&) non-virtual.
Removed unused Base64 functions in OTCrypto.
Added -Woverloaded-virtual to PEDANTIC_CXX_FLAGS
Merge pull request #286 from benma/cleanup

Removed unused (and hidden) base functions
README: Add license badge
Merge pull request #289 from lclc/readme

README: Add license badge
git hook: use printf for diff pritn out

Clang-format diff is not written out correctly if the code contains '\n'. The new line is interpreted by echo.
Merge pull request #287 from mhamrle/git_hook_escape_backslash

git hook: use printf for diff print out
OTASCIIArmor: remove (Get|Set)(AndPack)?StringMap

This is unused code that bloats the interface.

The class already allows armoring arbitrary byte arrays. Supporting arbitrary
data structures here makes no sense. In this case it creates a hard dependency
on the storage subsystem.  The encoding into byte arrays should be chosen at the
call site.
ot_utility_ot: remove unused function
OTRecordList: replace helper function with lambda
OTAsymmetricKeyOpenSSL: move undeclared function to unnamed namespace
opentxs-core: fix -Wmissing-declarations
Merge pull request #291 from OttoAllmendinger/pr-armoring-stringmap

OTASCIIArmor: remove (Get|Set)(AndPack)?StringMap
Merge pull request #290 from toxeus/fixMissingDeclarations

fix -Wmissing-declarations