Change to larger page sizes in spreadsheets

**Change to larger page sizes in grade spreadsheets**

**Summary**
Instructors want to see larger page sizes (more students per page) in grade spreadsheets

**Fix**
* Remove [15, 30,50] from list of options
* Change default page size to 100 students per page

**Tests**
* Ran test suite. There was one error that is associated with user permission that was present on a clean repo clone.
* Manual tests
  * Open spreadsheet and saw that the default page size was set at 100. Checked to see that the dropdown is in the range 100 to 1000.
  * Created a new spreadsheet and checked page sizes.