Add base functionality to use Find by tags

[maahir-garg]

Fixes #41

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Files with missing lines	Coverage Δ	Complexity Δ
...java/seedu/address/logic/commands/FindCommand.java	100.00% <100.00%> (ø)	6.00 <0.00> (ø)