Place Bisq AGPL license header at top of all Java sources

All `.java` files should adhere to the following template:

```
/*
* This file is part of Bisq.
*
* Bisq is free software: you can redistribute it and/or modify it
* under the terms of the GNU Affero General Public License as published by
* the Free Software Foundation, either version 3 of the License, or (at
* your option) any later version.
*
* Bisq is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public
* License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with Bisq. If not, see .
*/

package bisq.example;

public class Example {
}
```

Note the single blank line between license header and `package` statement and between `package` and `class` declaration.

Search the repository for every `.java` file and compare each file's opening comments, package statement, and class declaration with the license template in the issue. Add the specified header and preserve one blank line before the package and class declarations, then verify that all Java sources follow the same layout.

Written by the indexing model from the issue text.