Added a button for displaying the YaST logs

[lslezak]

Problem

• It should be possible to easily see the YaST logs from the UI to make debugging easier
• Related to gh#[service][web] Allow downloading logs from web UI #379

Solution

• Added a new button which opens a popup with the y2log file
• So far a simple solution, no message colorizing or filtering. We can improve it later.

Testing

• Tested manually

TODO

• Unit tests

Screenshots

Options Menu	Log Popup

[coveralls]

Coverage: 76.831%. Remained the same when pulling c4caae7 on show_logs into a28b018 on master.

[dgdavid]

Thanks @lslezak!

The approach looks good and simple as a first step for having an easy way to check the logs. However, I have left a few suggestions, please check them before going for the unit testing.

Thanks!

[dgdavid]

Looks great, just a few comments

[dgdavid]

LGTM 💯