Export text file name changed

the description of deliverable 1 of the project specifies the export
file to be named model.txt. the driver has been adjusted to meet this
requirement.
new SpamChecker constructor and file classification

- added constructor that takes a text file of a SpamChecker model
(likely the exported model of a previous SpamChecker object)
- added classifyFile() method to SpamChecker which created a
ClassifedDocument object (class added in this commit) for the file at
the specified path
Merge branch 'master' into skyler

Conflicts:
	Driver.java
	SpamChecker.java