* added signalmessenger integration
* allows to send a message (with an attachment) to one or more
recipients
* added signalmessenger documentation to manifest file
* remove debug logging from signalmessenger integration
* add signalmessenger to .coveragerc
* fixed typo in signalmessenger manifes
* moved service specific code to own pypi library
* updated pysignalclirestapi dependeny in manifest.json
* added pysignalclirestapi requirement for signalmessenger component
* fixed typo in codeowners
* reworked signalmessenger integration based on code review input
* updated requirements for signalmessenger
* small code improvements in signalmessenger integration
* no need to use the get() method to access dict parameters that are
required
* small changes in signalmessenger integration
* re-ordered import statements
* removed empty "requirements" list (not needed)
* changed import order in signalmessenger integration according to PEP 8
* used isort to order includes in signalmessenger integration
* renamed signalmessenger to signal_messenger
* renamed signalmessenger to signal_messenger in CODEOWNERS file
* changed documentation url in signal_messenger integration to new name
* changed signal messenger naming in .coveragerc
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