Add password for deletion

[wn]

Fixes first point of #40

Instead of confirming, require password.

Fix #63

[coveralls]

Pull Request Test Coverage Report for Build 251

• 11 of 12 (91.67%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.03%) to 92.473%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/main/java/seedu/address/logic/parser/DeleteCommandParser.java	9	10	90.0%

Totals
Change from base Build 245:	-0.03%
Covered Lines:	1548
Relevant Lines:	1674

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💛 - Coveralls

[OrangeJuice7]

The "parameters" and "example" are not consistent with the other commands. Either do
"Parameters: INDEX (must be a positive integer) PASSWORD\n"
"Example: " + COMMAND_WORD + " 1 12345"
or
"Parameters: " + PREFIX_INDEX + "INDEX (must be a positive integer) " + PREFIX_PASSWORD + "PASSWORD\n"
"Example: " + COMMAND_WORD + " i/1 x/12345"