[enhance](*) introduce alert manager

[cosven]

• introduce alert manager
  • show_msg when there is a ConnectTimeout currently
• show error message in search page

[coveralls]

Pull Request Test Coverage Report for Build 13138954848

Details

• 40 of 82 (48.78%) changed or added relevant lines in 8 files are covered.
• 3 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.04%) to 55.814%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
feeluown/gui/widgets/login.py	0	1	0.0%
feeluown/player/playlist.py	1	4	25.0%
feeluown/library/library.py	12	19	63.16%
feeluown/gui/components/search.py	0	14	0.0%
feeluown/alert.py	15	32	46.88%

Files with Coverage Reduction	New Missed Lines	%
feeluown/task.py	1	92.41%
feeluown/gui/components/search.py	2	21.67%

Totals
Change from base Build 13108953604:	-0.04%
Covered Lines:	10234
Relevant Lines:	18336

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💛 - Coveralls