Xxh-xxh

**xxh**
* Added support openssh versions <7.6
* Added realpath check
* Fix "local variable 'host_xxh_home' referenced before assignment"

**xxh**
* Added `+c SSH_COMMAND` argument to support ssh wrappers like [repassh](https://github.com/dyuri/repassh)

**xxh**
* Complete support AppImage
* Added package management arguments `+I +L +RI +R`
* New package source string format `xxh-(shell|plugin)-<name>+(git|path)+(url|path)`.
Example: `xxh myhost +I xxh-shell-sample+git+https://github.com/xxh/xxh-shell-sample +s xxh-shell-sample`.

This allows use package management arguments in config `~/.xxh/.xxhc`:

hosts:
myhost: settings for myhost
-p: 2222 set special port
+s: xxh-shell-zsh set zsh shell
+I: xxh-plugin-zsh-ohmyzsh install xxh-plugin before connect
+e: ZSH_THEME="clean" set ohmyzsh theme

**xxh**
* Fix xxh home and config logic

**xxh**
* Fix `xxh +I` behavior

**xxh**
* Removed `xxhp` tool
* New xxh arguments to manage packages:

usage: xxh [+I xxh-package ...] [+L] [+RI xxh-package ...] [+R xxh-package ...]

It's the next step to `xxh.AppImage`.

**All xxh-packages**
* Fix quiet mode