Strip tabs and trailing white spaces, and fix end of files (#748)

* format: Strip trailing whitespaces

We want to get rid of trailing whitespaces completly as they make just git
noice. Much better to start using automated tools to get rid of them once and
not getting them back again. This way git history will be cleaner and review
easier.

Commit was generated with:

    pre-commit run --all-files trailing-whitespace

* format: Files should have exactly one new line end of them

It is good practice that every file has one new line. It is not now days so
mandatory but it also is not nice if file has lot of newlines end of it. We will
use pre-commit which takes automatically care about this so let's fix all.

Commit was generated with:

    pre-commit run --all-files end-of-file-fixer

* format: Convert tabs to spaces

Project mostly use spaces over tabs. When mixing tabs and spaces this usually
makes formatting issues and also when changing those in commits it will make lot
of git noise. We will force spaces most of the time and use pre-commit to fix.

Commit was generated with:

    pre-commit run --all-files remove-tabs

---------

Co-authored-by: Kari Argillander <kari.argillander@fidelix.com>

apps/gateway/gateway.h

@@ -1,6 +1,6 @@
 /**
  * @file
- * @brief Header for example gateway (ie, BACnet Router and Devices) 
+ * @brief Header for example gateway (ie, BACnet Router and Devices)
  * using the BACnet Stack.
  * @author Tom Brennan <tbrennan3@users.sourceforge.net>
  * @date 2010
@@ -11,7 +11,7 @@
 
 /** @defgroup GatewayDemo Demo of a BACnet virtual gateway (multiple Device).
  * @ingroup Demos
- * This is a basic demonstration of a BACnet Router with child devices (ie, 
+ * This is a basic demonstration of a BACnet Router with child devices (ie,
  * gateway) appearing on a virtual BACnet network behind the Router.
  * This is an extension of the ServerDemo project.
  */