Few refactorings after playing around

 * moves gas-law related activities and classes into own subpackage [gaslaws]
 * adds ChemistryHelpTest project which will be the testbed for the tests
 * makes GasLaws activity load the contents of the ListView from XML file (res/raw/gas_laws.xml)
 * renames project directory from "Chemistry Help" to "ChemistryHelp" (removes space)
 * few minor changes