Fixed XSS vulnerability in week 3

[felixschorer]

Fix for #23:
Added input validation to both google sheets projects in week 3 to prevent cross site scripting attacks.
In week3-apis-data/09_google_sheets/sketch.js:

• Check if label is indeed a string with only alphanumerical characters and spaces.
• Check if number is valid number with only digits, dots and commas.
• Check if timestamp has the format MM/DD/YYYY hh:mm:ss.
  0/99/2017 8:61:93 would also pass the check despite not being a valid timestamp.

In week3-apis-data/10_google_sheets_madlibs/sketch.js:

• Check if the replacement text only contains letter, digits and basic punctuation, as well as spaces.
  If a replacement text fails the test it will redraw a new one.

[shiffman]

Thank you so so so much for this!