Factor out Policy Names

[TonyValenti]

Factor out Policy Names
Change AppDomain to AppContext (AppDomain just passes it through to AppContext and AppDomain is basically considered legacy).

[hishamco]

If @sbwalker agree with this change I'd like to use static readonly field instead of const

[TonyValenti]

You can't use static readonly in attributes though. Ie.:

        [HttpGet("{id}")]
        [Authorize(Policy = PolicyNames.ViewModule)]
        public List<HtmlTextInfo> Get(int id)
        {
            var list = new List<HtmlTextInfo>();
            try
            {
                HtmlTextInfo htmlText = null;
                if (_entityId == id)
                {
                    htmlText = _htmlText.GetHtmlText(id);
                    list.Add(htmlText);
                }
            }
            catch (Exception ex)
            {
                _logger.Log(LogLevel.Error, this, LogFunction.Read, ex, "Get Error {Error}", ex.Message);
                throw;
            }
            return list;
        }

[hishamco]

You are right I didn't notice they are using there