Fixed configuration window, improved data insertion into spreadsheet

* The configuration screen was to small to show the input fields, fixed that.
* On the config screen, only the two OAuth values were prefilled with existing values, other fields were always in their initial state, which was kind of confusing. Fixed that as well.
* When pulling new data starting from a different date, old data was overwritten. Added a function to search for the right row to insert new data into. Might still have some issues, like when going from a smaller to a bigger period, but other than that it worked fine for me. 

This allows to do an initial "big" import, getting all your old data, and then only work with relatively small periods to append new data to the end of your spreadsheet.