LDEV-4391 Update jQuery to version 3.3.1. Add Migration Plugin. jQuery was upgraded to version 3.3.1. It was put into jquery.js file which is referenced by LAMS JSPs. In the same file below jQuery code Migration Plugin 3.0.0 was pasted. This way it gets loaded every time jQuery gets loaded without extra HTML tags. The Migration Plugin reintroduces API removed from jQuery 3. This way we can benefit from jQuery 3 efficiency and security and do not have to use everywhere its new API straight away. jQuery and Migration Plugin in jquery.js are in their compressed, production version. The Plugin produces only debug information in JS console: "JQMIGRATE: Migrate is installed, version 3.0.0". It appears every time the Plugin gets loaded. We can silence this message if we want to. In jquery.migration.js the two above scripts come in their development version. The Plugin produces warnings every time deprecated API is used, pointing to spots which require rewriting to comply with jQuery 3 new API. While production jQuery + Plugin solution seems to work fine, we should ultimately aim at rewriting our code and sticking to pure jQuery 3. During development jquery.migration.js contents should be copied to jquery.js to enable warnings.