Cart/Order Item Preambles

Contributions:

1) Preambles

Title preambles can be used by extensions to add information before product titles.
This is useful in cases where cart/order items are the "values" of parent
product properties (e.g. Composite Products extension - https://trello.com/card/composite-products/4eea190569963dd4135c83f3/321).

Hooking into the title itself to add this information will not suffice, because preambles should be nested in their own html block, outside the link anchor tags of product titles.

Example: A computer is added to the cart and
"Product X" is the chosen option for a "Mainboard" property. The
preamble allows developers to add a formatted "Computer Mainboard: "
string before the product title, where 'Computer' is the name of the
parent product/collection and 'Mainboard' is the property that this product corresponds
to.

Example 2: http://www.somewherewarm.net/PreamblesEx.jpg ( Title 1/2/3 = Property Preambles of the 'BTO' Composite Product. The products are listed right below, as usual, with their corresponding quantities. )

2) Filters

The 3 other commits are minor additions to keep consistency with other action / filter hooks. There is also a filter added to the dashboard recent orders widget item count (there have been requests to adapt the reported number of order items reported in the case of Product Bundles)

Note that the existing code only counts line-items and does not take into account the line item quantities. So, technically, the item count is not accurate as it is. Not sure if this is intentional or not.