all: Introduce limits for custom goals

This commit introduces the following limits:
* 32 characters for names of goals and labels
* 50 expected copies for goal

This is because:
* probably no one needs 51 copies of data or really long names of goals
* our code doesn't handle huge strings (eg. because of limits for
  length of network messages) very well
* our code doesn't handle too many number of copies of chunk -- in many
  places this number is kept on uint8_t variables
* it would be easier to create usable CGI GUI when strings are not too
  long

Change-Id: I2815919eba0a6d2e18fc38818950bd431a1845b1