Remove indenting from sources that start indented

[NicksPatties]

When starting an exercise that is indented (like trying to grab a function that is indented from within a class), the user has to type the indentation before actually typing the exercise.

54-starting-exercise-with-indent.mp4

This could also be related to adding exercises to sweet as well. When adding an exercise from STDIN, when writing a new file, I should remove any leading whitespace from the file, and remove that amount of whitespace from each line that is added to the file.

[NicksPatties]

I added the DedentLines function in #90 , but piping stdin into sweet does not use that yet