general improvements; fixing several issues reported by users

• adding CK_PYTHON env variable in ck script to let user select required python version (python or python3)
• automatically detecting python3 or python on Linux
• fixing license of a php OpenME code - now the same as CK (tiny part to connect PHP-based web requests to CK)
• adding 'find' function to 'repo' module and changing default behavior. Now "ck find repo:" returns path to repository rather than to meta. To return path to meta, use "ck find repo: --meta". Closes ticket #45
• automatically detecting server host and port, if used! Closes ticket #38
• adding zip action to CK kernel, to simplify archiving of entries, i.e. "$ ck zip (repo wildcards:)module wild cards:"
• when copying entry, changing date and CK version (fixing #39)