Refactor the corner view visibility

[MGaetan89]

I've refactored the AbstractTableAdapter#setAllItems method and added some tests for the corner view logic (creation and visibility).

This change fixes an issue where the corner view could remain visible when toggling TableView#mShowCornerView from true to false.

[Zardozz]

There is two problems with this pull request.

1. AbstractTableAdapterTest class is really in the wrong directory, it should be located under the "test" directory (have a package name of "com.evrencoskun.tableview.test"), this might not currently affect the tests but it is not the correct structure for this type of test.

The reason it should be under the "test" directory and package name of "com.evrencoskun.tableview.test" is that androidTest auto generates the androidTest resources under the "com.evrencoskun.tableview.test" thus making it hard to use them if not in the right package (though this class does not use them at the moment so it works).

2. The change breaks the fix for Corner View not shown #308 for which you fixed by altering the tests by inverting there assertions in the CornerViewTest

setShowCornerView method is to set a Flag to change the behaviour of setAllItems without breaking the current behaviour

testColumnHeadersOnlyTableShowCorner and testColumnHeadersOnlyTableShowCornerResetEmptyTable and testColumnHeadersOnlyTableShowCornerResetNonEmptyTable Tests
set the cornerView to be shown even if they have no row data or row headers but do have column header data.

These tests in CornerViewTest need to pass without any changes to the tests.

The idea of the tests

// Set the option to show corner view when there is not row data
       tableView.setShowCornerView(true);

is the cornerView is created (i.e. Not Null) Assert.assertNotNull(cornerViewReset);

even when there are no rows

// Only want column headers
        SimpleData simpleData = new SimpleData(5, 0);

basically if setShowCornerView is true then the test in your code of boolean hasRowHeaders = rowHeaderItems != null && !rowHeaderItems.isEmpty(); should be ignored (or always return true)

[MGaetan89]

Thanks for having a look at my PR. Indeed my approach was originally wrong.
I've updated my PR, so now the original tests remain unchanged, and it still fixes a couple of corner view visibility.

[MGaetan89]

@evrencoskun any chance to have a look at this?