Instruction Modals

I still need to add the ability to link a series of instruction modals. 

Modals styling and alignment are functional. Start a game and enter:
`showInstructModal('#inventory', 'instruct-bottom', 'align-left', 'Hello!');`
in the browser java console.

**TODO:**
Modals still need to be re-aligned when browser window resizes.
Need to check if modal is too big for the alignment.
'Next' and 'Exit' button functionality.