Impose proper order for constructors and derived functions

[jeltsch]

Currently, the definitions of the process family constructors and of the functions derived from them come in suboptimal order. The same is true for various kinds of lemmas about them. We shall impose the following order for the definitions of the above-mentioned functions as well as for the lemmas about them within every block of such lemmas:

1. Constructors
   1. receive
   2. parallel
   3. new_channel
2. Derived functions fundamental for implementing things related to the constructors
   1. create_channel
3. Other derived functions
   1. repeated_receive
   2. general_parallel
   3. guard