Implement Sizeable for table component and better support for ajax implementation

[vaadin-bot]

Originally by @mstahv

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Subtasks:

• implement Sizeable
• add optional variables (as per meeting on fri 26.1.)
• firstrow (first row from which client wants new uidl, not necessary firstvisible, but defaults to this)
• rowsPerRequest (amount of rows client wants to read, defaults to pagelength)

This way client gets by default same data as previously, but can:

• get cache rows as it wants (hinted by sizeable values)
• and update values (firstvisible, selected etc) without receiving pagelength of already rendered rows from server

[vaadin-bot]

Originally by @jojule

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Added "rows" unit to Sizeable interface.

Will add Sizeable implementation to Table on java side.

[vaadin-bot]

Originally by @mstahv

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Assigning this to Joonas and wrote down notes from design meeting.

[vaadin-bot]

Originally by @jojule

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Implemented this on serverside. Added optional height and width attributes to table uidl-tag. If size is not specified, client-side can automatilly decide it. Values are of the format "100px". Supported units are px and %. Furthermore height also supports rows.

[vaadin-bot]

Originally by @jojule

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For beta-1, keep it simple and possibly leave it incomplete.

[vaadin-bot]

Originally by @mstahv

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in [458]

Removed percentage and row units.