Obtain certificate button of key-store runtime view should use a new alias

In the runtime view of elytron key-store, in the "Aliases" sub-view, there is a "obtain" button that uses an already created alias, but this is wrong. The "obtain" command should ask for a new alias, so the retrieved certificated obtained from LetsEncrypt should be placed in a new alias.

The change is to move the "Obtain" button from the "Aliases" sub-view to the Key Store table (parent view) and make the "alias" attribute writable.