Basic support for schema editing

[jan-martinek]

It would be nice to have a basic support for altering db tables – to be able

• to create a new table (automatically created with autoincremented id)
• to add a column to existing table (int, varchar, text, enum)
• to add an option to enum field
• to hide a column (via column comments?)
  • I'd refrain from deletions
  • this would require removing those columns from query results in entries (something like this create temporary tabletempselect * fromexample_course;
show full columns fromtemp;
    works for multiple tables)