Merge pull request #2 from semlak/addExpenseCategory

[semlak]

added category to expense, added monthly and category charts, althoug…

[semlak]

This might not be ready to merge in yet. I added an category field to the expense category, and cleaned up some of the other code satisfy eslint. However, the createForm for expense field for the category doesn't allow you to create a new category, it selects from existing categories, which unfortunately would be none unless you have manually populated your database with transactions with categories, which is what I did. RIght now, though, the program checks to see if you don't have any categories in your data, transactions, and then hides the category column in the trxn table so it doesn't look too bad. I also added a chart displaying monthly data and a pie chart that shows the categories, but you have to enable them in the source code to get them to display.