Remove template matching and pseudo opcodes

The current code contains a rather complex script template matching engine,
which is only used for 3 particular script types (P2PK, P2PKH, multisig).
The first two of these are trivial to match for otherwise, and a specialized
matcher for multisig is both more compact and more efficient than a generic
one.

The goal is being more flexible, so that for example larger standard multisigs
inside SegWit outputs are more easy to implement.

As a side-effect, it also gets rid of the pseudo opcodes hack.

src/script/script.cpp

@@ -141,11 +141,6 @@ const char* GetOpName(opcodetype opcode)
 
     case OP_INVALIDOPCODE          : return "OP_INVALIDOPCODE";
 
-    // Note:
-    //  The template matching params OP_SMALLINTEGER/etc are defined in opcodetype enum
-    //  as kind of implementation hack, they are *NOT* real opcodes.  If found in real
-    //  Script, just let the default: case deal with them.
-
     default:
         return "OP_UNKNOWN";
     }