Re-organize the reserved words for Swift4

[ehyche]

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• [x ] Read the contribution guidelines.
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Description of the PR

There was a previous issue (#6919) and subsequent PR (#6952) to add "throw" to the list of reserved words for Swift 4.

I decided it would be helpful to group the Swift4 reserved words into groups that we can check against future revisions of swift. For each group, I provided a reference link so that we can check in the future if new reserved words have been added. I verified that all of the current reserved words are included somewhere in the new groupings. The groups are:

• Reserved words specifically called out in the Swift 4 Language Reference (link provided in the source)
• Reserved words from the Swift Standard Library (link provided in the reference)
• Objective-C compatibility types
• Commonly-used Foundation types
• Others

[ehyche]

@jgavris @Edubits @jaz-ah : please review

[wing328]

@ehyche when you've time, can you please update the following test as id has been added to the list in this PR?

Results :

Failed tests: 
  Swift4ModelTest.simpleModelTest:42 expected [id] but found [_id]

Tests run: 544, Failures: 1, Errors: 0, Skipped: 3

[wing328]

@ehyche no worry I've fixed the test.