Support Windows 10 1903 Light Theme

When launch from test framework, the Application.StartupPath looks like "C:\PROGRAM FILES (X86)\MICROSOFT VISUAL STUDIO\2019\COMMUNITY\COMMON7\IDE\EXTENSIONS\TESTPLATFORM" which may not have write permission.

Support local IPv6 listener

# Conflicts:
#	shadowsocks-csharp/Model/Configuration.cs

Turn off per-monitor DPI awareness as it is not supported

Fixed bug of #2379 pullrequestreview-254461303
Redundant paintings when user move mouse on the icon, pixel by pixel.

Move GetWindows10SystemThemeSetting() to Util.cs
WindowsThemeMode use enum
Status var windowsThemeMode rename to windowsThemeMode
Used `if else` to replace `switch case`
Delete legacy commint (Some code).
Increase contrast for icon.

Added Config Form hint text

Add new hints and fixed some old interaction bugs

Fix udp relay

fixed issue #2371

Support Windows 10 1903 Light Theme (Menu icon color)

Plugin arguments tooltip

When error code is SocketError.AccessDenied/10013(WSAEACCES), the port is reserved by system and you may not find the process name in `netstat`.
 https://github.com/shadowsocks/shadowsocks-windows/issues/1835#issuecomment-453528715

Add check box to toggle plugin argument input

Removed unused array allocations

Improve the code readability useProxy test condition

Mentioned in PR #2219

Marked ApplicationRestartFlags with Flags attribute