Rearrange layout of dock widgets.
Replace QLabels with read-only QLineEdits in BlueprintCalculatorWidget
to avoid freeze and flickers during price updates.

Rearrange layout of MainWindow.
Rename marketNetwork to priceNetwork.

Add ordersNetwork to fetch market orders.
Rename skill_requirement_tree.cpp -> skillrequirementtree.cpp.
Rename skill_requirement_tree.hpp -> skillrequirementtree.hpp.

Remove the previous root item (i.e. the type name) in
SkillRequirementTree, now top-level skills will be roots in the tree.
Add AttributeTree.

Combine all tabs in ItemDetailsWidget involving attributes into one
"Attribute" tab, and use an AttributeTree to group and display them.