apache-frontend: update TODO

apache-frontend: Update TODO

software/apache-frontend/TODO.txt

 Apache:
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-- set a redirection of / in option
-- Implement support of multiple ip (if possible) for multiple ssl (other solution is to ask master instance but quid to much apache process?)
 
-Squid:
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-- Only cache in ram. Problems with to much squid on the computer or too many slave?
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-SlapOS:
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-- Implement intelligent apache graceful -> Should check slave configuration and return error to slave if there is a problem (important but difficult)
-- useless srv/squid_cache directory so far