Data directory, config file and default wallet support:

* Under Linux, data directory is '~/.mmgen'; config file is 'mmgen.cfg'.
 * If default wallet is enabled, specifying the wallet on the command line is
   no longer necessary.  If not, all MMGen commands behave as previously.
 * The datadir structure mirrors that of Bitcoin Core: mainnet and testnet
   share a common config file, but testnet puts its other files including its
   default wallet in a separate subdirectory 'testnet3'.

New routines have been added to the test suite to test these features.
Tested only under Linux.

scripts/deinstall.sh

@@ -1,6 +1,6 @@
 #!/bin/bash
 
-CMD='rm -rf /usr/local/bin/mmgen-* /usr/local/lib/python2.7/dist-packages/mmgen*'
+CMD='rm -rf /usr/local/share/mmgen /usr/local/bin/mmgen-* /usr/local/lib/python2.7/dist-packages/mmgen*'
 
 if [ "$EUID" = 0 ]; then
 	set -x; $CMD