Changed heat coefficient from alpha to u

[EPrade]

changed "alpha_w_per_m2k" to "u_w_per_m2k":

• changed tutorials
• added district heating standard pipes
• added"u_w_per_m2k" in std types for pipes
• added deprecation warning for alpha

Not sure how to handle the version and format version. Since i changed the format I need to change the format version. Do I also need to change the "normal" version? After the pull request develop would then be on a new version