Paths to js/css resources

[aozalevsky]

Some problems of #23 were caused by inaccessible paths to static js/css resources. Looks like there are some duplications and version mismatches that require refactoring. Overall it would be better to simplify a set of resources and sync it with layout.html.

E.g. about_validation.html and validation_help.html have a somewhat mixed set of links.

 <!-- add Javasscript file from js file -->

            <script type="text/javascript" src="js/jquery.min.js"></script>
            <script type="text/javascript" src="js/bootstrap.min.js"></script>
            <script type="text/javascript" src="js/main.js"></script>
            <script type="text/javascript" src="js/jquery-3.3.1.min.js"></script>
            <script type="text/javascript" src="js/popper1.12.9.min.js"></script>
            <script type="text/javascript" src=".js/bootstrap4.1.3.min.js"></script>
            <script type="text/javascript" src="js/bootstrap3-typeahead.min.js"></script>

[aozalevsky]

substantial cleanup is done dev_2.0 branch. it's not final yet, so I'll keep the issue open for a while.