Refacoring and minor fixes

Description

This patch includes a series of fixes for a general refactoring

• Headers reorganization and cleaning
• Translation fixes demanded through Weblate
• Fix #2739 (closed) - Send clipboard as keystrokes

Related Issue

• #2739 (closed) - Send clipboard as keystrokes

Motivation and Context

Cleaning up Remmina code, and fix some annoying bugs

How Has This Been Tested?

With a lot of local tests, that will surely not contemplate most of the real life use cases :-)

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.