Added is_sole function to publications
added sole author to author publication table, as well as tests for author publication table and Appearance by author table.
Added code for sole appearance for each type of publications in appearance page
Merge remote-tracking branch 'origin/SoleAuthor' into SoleAuthor

Conflicts:
	src/comp61542/database/database.py
	test/test_database.py
Merge branch 'SoleAuthor' of https://github.com/TeamBeedle/comp61542 into SearchAuthor