Make idProperty configurable.
Instances of SlickGrid should not share one global EditorLock by default.

When SlickGrid is used as a part of an editor inside another SlickGrid,
sharing a global editor lock will close the editor unexpectedly.
fixed CSS url in unit test pages
made sure all examples show the full function interface of getItemMetaData - this is for coder awareness only
- augmented a few unit tests for grid: making sure event UNsubscription works as expected

- added a few unit tests for dataview: some minimal grouping tests

- test data is generated using a cloned implementation of the Mersenne Twister to provide a 100% predictable semi-random data set: the 100% predictability ensures that all test platforms will produce (and test) the exact same (semi-random) data; this also helps debugging in case of test failures
- fix: removed illegal double UI sort handler definition for $headers

- improved the heuristic for getRowPosition(row) so it approaches O(1) for a range of variable rowHeight using grids

- made sure all getItemMetaData() calls fill in all function parameters (row, cell), so that anyone can be sure that `cell` is either a valid cell index number or the boolean `false` when the call is made without any knowledge about the to-be-addressed column in said row.

- inserted a few assert()ions to validate assumptions (TODO: create a filter which removes these calls -- and the implicit dependency on lib/assert.js -- for production files); I find that using this rather classic approach to testing/validating is a great boon next to (unit) testing as the assertions are 'live 24/7' during the entire development phase/cycle.

- getDataItemValueForColumn() now also receives row and column metadata so that metadata providers (via DataView or directly) can provide customized column data extractors on a per-row and per-column basis: this is very useful to construct customized 'grouping'-enabled DataView-based grid layouts.
- made the CheckCountAggregator and DateRangeAggregator .accumulate() function implementations match those of the other aggregators: the DataView accumulator compiler can handle these perfectly well and they make for easier debugging and readability when these are not compiled (yet).

- updated the documentation comment chunk for the metadata provider options
Merge remote-tracking branch 'remotes/ciel-yu/dev' into k0stya-rowspan

Conflicts:
	slick.dataview.js
	slick.grid.js
quick hack to see the call stack when a unit test fails -- TODO: make sure my more organized qUnit patch works out well, like this.
fixed several examples and examples index page