Synchronize the password validation regexp with other SDKs / ICONex

Special characters from the password validation have been updated in ICONex and T-Bears. The Python SDK also needs to be updated in order to reflect these changes :

https://github.com/icon-project/t-bears/pull/25
https://github.com/icon-project/iconex_android/pull/4
https://github.com/icon-project/iconex_chrome_extension/pull/12
https://github.com/icon-project/iconex_ios/pull/4

icon-project / icon-sdk-python

Synchronize the password validation regexp with other SDKs / ICONex #19