misc: use self.logger in the spiders

[szymonlopaciuk]

Description

This is to unify logging mechanisms used in the spiders. Previously some spiders used self.log.

In some cases (spiders.common.*) spiders create the logger independently via logging.getLogger. I am leaving this, as it provides additional debugging information to know that the message comes from the superclass.

Related Issue

Closes #183.

Checklist:

• [x] I have all the information that I need (if not, move to RFC and look for it).
• [x] I linked the related issue(s) in the corresponding commit logs.
• [x] I wrote good commit log messages.
• [x] My code follows the code style of this project.
• [x] I've added any new docs if API/utils methods were added.
• [x] I have updated the existing documentation accordingly.
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.