Improve Vector CopyConstructor test

- First make sure the copy is a copy
- Then edit each copy and make sure the copies' edits don't affect each
  other
Remove unnecessary doubles of lab instructions
Rename test OperatorBracket to OperatorBracketWrite
Whitespace: Add space around binary operators
Fix off-by-one errors in Insert tests
Add InsertALotOfItems test
Implement Vector<T>::insert(size_t index, const T& element)
Update max_size in increase_memory

I can't think of a way to test this, as it's a private, internal
implementation detail.
Implement Vector<T>::push_back(const T& element)
Implement Vector<T>::erase(size_t index)
Implement Vector<T>::clear()
Implement Vector<T>::exists(const T& element)
Implement Vector<T>::sort(bool ascending)
Sort vector descending in SortUniqueDescending test
Implement Vector<T>::unique_sort(bool ascending)