Autofill contents when subscribing

[qjqqyy]

Changes

Autofills title and description when subscribing to feed. Resolves #46

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While here also slightly refactor Autofill API:

• Autofill now is constructed with an Entry (instead of Title and Description)
• Autofill finishes its job with a getFilledEntry() which returns Entry

[coveralls]

Pull Request Test Coverage Report for Build 779

• 15 of 36 (41.67%) changed or added relevant lines in 5 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.6%) to 83.062%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/main/java/seedu/address/logic/commands/SubscribeCommand.java	0	9	0.0%
src/main/java/seedu/address/model/entry/util/EntryAutofill.java	8	20	40.0%
<!--	Total:	15	36	41.67%	-->

Files with Coverage Reduction	New Missed Lines	%
src/main/java/seedu/address/model/entry/util/EntryAutofill.java	1	73.21%
<!--	Total:	1		-->

Totals
Change from base Build 770:	-0.6%
Covered Lines:	2089
Relevant Lines:	2515

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💛 - Coveralls