test.project() tests all files in tests directory

Currently running test.project does nothing on a default project, which makes it appear to be broken

Original implementation used testthat's test_directory() function
This required that all test files be prefixed with test-

Adding this prefix is distracting since all code is in a tests directory already

Instead grab all files in tests directory and send to test_file()

Set enclosure environment for test_file

test_file() assumes that we are testing from the global environment
Since we are testing within a function, we need to pass the function's environment as the enclosure

removed test.project from minimal test since there are no tests available in a minimal project
Also test_dir was throwing an error with testthat_0.8 since the tests director was not available
for setwd()

Explicitly get package test variables from globalenv()

testthat runs it's tests in a new environment
ProjectTemplate runs the data readers in the global environment
For package tests to work, variables must be fetched explicitly from the global environment

Rather than litering the code with environments, set the GlobalEnv to be the parent of the test environment
Set all functions to use inherits = TRUE for defaults

This ensures that GlobalEnv is in the search path for all functions