Use a QVector instead of a QList

Use a QVector instead of a QList

This makes the code go quite a bit faster (saves ~7-8% of the
total amount of instructions executed when running crypto.js

Change-Id: I6b3bd08eca98b45593262e2fc6e0ce5056257e76
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>