Add option to lock pricing

Add an option to enable a pricing lock for a certain item or category, preventing any user (with the exception of Admin), from changing the cost, sale price etc.

Why? I want to prevent colleagues to change the prices of our service products, hourly rates etc. The quote approval function doesn't completely cover this, because i don't want to have to approve ALL quotes with one of these line items included, regardless of price. Also, the max. discount part can be mitigated.