Improvements of _File and FieldTest_File

_File:
- small changes to beginning documentation
- modified printSpeedTests to printTests. It also now loops through
self.Tests[“NUM”], as this list will store all of the tests in order by
test number
- simplified __str__

FieldTest_File:
- updated comments at top
- updated imports
- beginning of __init__ checks if the file at filePath is a legitimate
FieldTest File (looks for “CPUC Tester”)
- loadFieldTestInfo() parses all necessary information
- end of loadFieldTestInfo() calculates the average latitude and
longitude based on all of the measurements throughout the file.