Add Row constructor and fix javadocs

[alvarezguille]

Also added missing braces and minor javadoc improvements

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This change is 

[rogozinds]

Reviewed 2 of 3 files at r3, 1 of 1 files at r4. Review status: all files reviewed at latest revision, 2 unresolved discussions.

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addon/src/main/java/com/vaadin/board/Board.java, line 22 at r4 (raw file):

consists on Wrong preposition, either based on or consists of https://english.stackexchange.com/questions/61600/consist-in-vs-consist-of

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addon/src/main/java/com/vaadin/board/Board.java, line 25 at r4 (raw file):

 * Each Row consists of four columns, and can contain up to four components
 * taking one column each, or fewer components with multiple columns each as
 * long as sum of columns stays less than or equal to 4

a dot at the end of the sentence

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Comments from Reviewable

[alvarezguille]

Review status: 2 of 3 files reviewed at latest revision, 2 unresolved discussions.

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addon/src/main/java/com/vaadin/board/Board.java, line 22 at r4 (raw file):

Previously, rogozinds (rogozinds) wrote…

> consists on Wrong preposition, either based on or consists of https://english.stackexchange.com/questions/61600/consist-in-vs-consist-of

Done.

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addon/src/main/java/com/vaadin/board/Board.java, line 25 at r4 (raw file):

Previously, rogozinds (rogozinds) wrote…

a dot at the end of the sentence

Done.

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Comments from Reviewable

[rogozinds]

Reviewed 1 of 1 files at r5. Review status: all files reviewed at latest revision, all discussions resolved.

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Comments from Reviewable