Implement attachment in Model, Serializer, Builder
Implement attachment in GUI
Change to HTML link for demo
API for attachment
Merge pull request #317 from evansb/attachment2

Attachment
Still buggy
Merge branch 'master' of https://github.com/cs2103aug2014-w10-1c/main into subtask-api

Conflicts:
	You-QueryEngine-Tests/query_tests.cpp
	You-QueryEngine/api.cpp