Ultraheat-api 0.5.0

Add support for the Landys+Gyr UltraHeat T550 model.

• The IR-interaction was changed slightly so that both the UH50 and the T550 respond well
• The T550 seems to return '/LUGCUH50' as a model name, which is returned as 'LUGCUH50' by the interface. So unfortunately no distinction can be made with the UH50 based on the model name. The variables that could be read are returned independendly of the model.
• The T550 returns usage as MWh, for which variables have been added to the interface.

Detailed changes:

• Add support for Landis+Gyr UltraHeat T550. The new meter is called LGUHT550 in code.
• Add heat_usage_mwh and heat_previous_year_mwh to the interface (only to be filled when returned by the heat meter)
• Add dummy test files
• Rename existing test file and add test file for UltraHeat T550
• Read meter data until "!"
• Remove no longer needed newlines from dummy.txt
• Remove extra whitespace and unneeded write \x2F\x3F\x21\x0D\x0A == /?!\x0D\x0A

Thanks a lot @blomqvist !