[repo] minor cleanups to bootstrap sequence * fix some docstring/comments * move initialization of HooksManager to the __init__.py, this has nothing to do with pool initialization / boostraping

[schemaserial] serialize additional yams parameter for customs type Yams have a new custom type feature. We add support for extra parameter on CWAttribute in schema serialization handling. Closes #2847151

[sql] preprocess_entity uses lgdb helper's SQL converters. The preprocess_entity does not yield anymore the conversion logic for different base types, but relies on a new SQL_CONVERTERS dictionary of the db helper. This will allow later inclusion of new base types.

[repo] kill rebuildinfered feature from Repository.set_schema This clutters thing and is useless in most cases: when schema just have been readen from the database or from the file-system, infered relations have just be calculated. The only use-case where it should be rebuilt is on migration (ie schema modification by editing the meta-model using rql), so move this feature there.

[test] stop deepcopying for nothing

drop xhtml content-type support (closes #2065651) * HTMLStream does not care about xml any more * reqquest.demote_to_html and .xhtml_browser are deprecated * web config: drop force-html-content-type option * adjust tests