Change delete command to use ID instead of index

[koonweee]

• Update delete command to use ID instead of index
• Update input validation for a valid ID (> 3 digits) instead of index
• Removed irrelevant test (Command exception became parse exception)

Resolve #55

[codecov]

Codecov Report

Merging #65 into master will increase coverage by 0.11%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master      #65      +/-   ##
============================================
+ Coverage     72.31%   72.42%   +0.11%     
- Complexity      400      402       +2     
============================================
  Files            70       70              
  Lines          1228     1233       +5     
  Branches        124      126       +2     
============================================
+ Hits            888      893       +5     
  Misses          308      308              
  Partials         32       32              

Impacted Files	Coverage Δ	Complexity Δ
...main/java/seedu/address/commons/core/Messages.java	0.00% <ø> (ø)	0.00 <0.00> (ø)
...va/seedu/address/logic/commands/DeleteCommand.java	100.00% <100.00%> (ø)	9.00 <1.00> (+2.00)
...java/seedu/address/logic/commands/EditCommand.java	97.01% <100.00%> (ø)	12.00 <0.00> (ø)
...eedu/address/logic/parser/DeleteCommandParser.java	100.00% <100.00%> (ø)	2.00 <1.00> (ø)

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