Prevent duplicate IDs and remove leading zeros

[koonweee]

• Add trims leading zeros from specified ID
• Tests and Typical Animals updated to match new ID format (no leading zeros, more than 3 digits)
  Resolves Prevent adding animals with duplicate ids #106

[codecov]

Codecov Report

Merging #116 into master will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##             master     #116   +/-   ##
=========================================
  Coverage     71.38%   71.38%           
  Complexity      423      423           
=========================================
  Files            74       74           
  Lines          1342     1342           
  Branches        133      133           
=========================================
  Hits            958      958           
  Misses          343      343           
  Partials         41       41           

Impacted Files	Coverage Δ	Complexity Δ
.../java/seedu/address/logic/commands/AddCommand.java	100.00% <ø> (ø)	8.00 <0.00> (ø)
src/main/java/seedu/address/model/animal/Id.java	80.00% <ø> (ø)	6.00 <0.00> (ø)
.../java/seedu/address/model/util/SampleDataUtil.java	68.75% <ø> (ø)	3.00 <0.00> (ø)
...in/java/seedu/address/logic/parser/ParserUtil.java	78.57% <100.00%> (ø)	13.00 <0.00> (ø)

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[aizatazhar]

Could you also change the error message (MESSAGE_CONSTRAINTS in Id.java) to mention that leading zeroes are not allowed?

Also need to change the default zookeepbook.json (in SampleDataUtil.java) animal's ids to have no leading zeroes