Adding warning to MaterialProperties for invalid keyword args

[timryanb]

• Since PR Making it easier to define orthotropic properties using MaterialProperties class #252 , invalid input args being passed to MaterialProperties change the default material type to orthotropic
• This can have unexpected behavior for users who accidentally misspell valid isotropic parameters
• To make the issue clearer the following changes have been made:
  1. Passing an invalid/misspelled argument raises an explicit warning
  2. Invalid arguments are ignored when deciding if the properties are orthtropic/isotropic