fixed feed caching logic for multiuser scenario

only vanilla feed data may be cached as every user may have different
fetched feed hooks to apply
deactivated FeedParser re-use as it is not multiuser safe

different users may have different fetch feed and feed fetched hooks
Merge pull request #353 from rangerer/feed_caching_fix

Feed caching fix
exception handler: remove report to tt-rss.org
handle_rpc_json: do not crash if net-alert is somehow unavailable
Revert "exception handler: remove report to tt-rss.org"

This reverts commit b55aec078c18b3db85d34329be3f01364e383667.
add ttrss version and init params to reports
make_init_params: add some additional information useful for reporting
update report to tt-rss prompt
exception_error: support objects in ext_info
make_init_params: add theme
make_init_params: add plugins
init params debugging: support objects etc
exception_error: always stringify ext_info