Improve plugin behavior classes/packages with no methods #516

[volivan239]

Description

• When choosing class with no methods available for testing, Generate tests with UTBot... is now disabled
• When launching plugin on a package with no methods found, Info message is now shown

Fixes #516

Type of Change

Please delete options that are not relevant.

• Minor bug fix (non-breaking small changes)

How Has This Been Tested?

Automated Testing

No new tests were added

Manual Scenario

• Try Alt+Shift+U while on a class with no methods -- nothing happens
• Try Alt+Shift+U on a package with classes that have no methods -- an info message is shown

Checklist (remove irrelevant options):

• The change followed the style guidelines of the UTBot project
• Self-review of the code is passed
• The change contains enough commentaries, particularly in hard-to-understand areas
• New documentation is provided or existed one is altered
• No new warnings
• Tests that prove my change is effective
• All tests pass locally with my changes

[Vassiliy-Kudryashov]

Should we return here?

[volivan239]

added return