FIX: some crash about thread-safe in statistics

[fixes #2542] Fix accidental index invalidation

Fixed an invalid index that was unexpectedly caused when the configuration was abandoned, resulting in an list box index exception.

Refine PAC server

- Uncompress the text file for better version control
- Touch the PAC files in first place

- Split the file operations to new PACDaemon
- More precise matching logic for handling PAC content http request

Modify PAC request behavior

Update the PAC file using the proxy channel only when proxy mode is enabled.

#2480 #1004

Fix shadowsocks/shadowsocks-windows/#2458

* Fix shadowsocks/shadowsocks-windows/#2458

* Servers List Box position adjustment is consistent with the v4.1.6 version

Add Experimental.md

issue_template: ask users to delete the instruction text

Support Windows 10 1903 Light Theme

留着每次读起来都很蛋疼，让用户看完就删了吧。

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.

Refactoring Config Form

Upgrade appveyor image to Visual Studio 2017

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