Convert to Yii log targets and use DbTarget

[timkelty]

Description

• Converts the existing custom logging to a Yii Log Target with a feed-me category.
• By default, logs will now be stored in the database (feedme_logs), as they are displayed in the CP.

Related issues

Fixes #1344

[angrybrad]

We'll need to update the install migration with the new log table for fresh installs.

[timkelty]

@angrybrad should be ready:

• added install migration
• added logging example
• added changelog line

[dgsiegel]

@timkelty it looks like that even with your example, logs will always be stored and read from the db. Adding the logging example will additionally log it to a file, correct?

[timkelty]

@dgsiegel That's correct.

[dgsiegel]

@timkelty in that case I'd urge you to review this merge request. Feed Me is quite noisy in its default configuration, and unless you set logging to false or error, that table will grow considerably if you import lots of items (10k+) regularly (few times per day).

Additionally, the README in its current form suggests that you are able to replace the default logging mechanism (and therefore also displaying the latest log entries in the UI), which is not the case.