Github project names

[rozyczko]

Currently we have a well defined split on the technique level
<technique>-app
<technique>-lib

On the general level, this isn't as clear cut since we have

• corelib
• guilib
• crystallography
• utils/utilities (planned)

Proposal:

rename:

corelib -> core
guilib -> gui-components
crystallography (no change)
utils (no change)