Fixed some PostgreSQL issues

[danthedaniel]

As for what this fixes:

• The user column needs to be escaped else Postgres will think it's the USER keyword. This was acknowledged in the schema file but not in the alert insertion statement in the C code.
• The schema file has some conflicting index names so I prefixed each with the name of the table it's for
• Many alerts do not match the schema defined, as they don't provide a user or src_ip/dst_ip, so I removed the NOT NULL constraints from those columns on the alerts table.

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There should also probably be a prompt in the install.sh script to ask users if they want Postgres or MySQL support in the application.

I didn't want to mess around with that behemoth of a script though.

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This change is

[danthedaniel]

I should also add that these changes were made with PostgreSQL 9.4 in mind.

[jrossi]

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Reviewed 3 of 3 files at r1.
Review status: all files reviewed at latest revision, all discussions resolved.

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Comments from the review on Reviewable.io

[atomicturtle]

We might need to revert this one, it is breaking mysql compatibility on :
"alert(server_id,rule_id,level,timestamp,location_id,src_ip,src_port,dst_ip,dst_port,alertid,"user",full_log) "

"user" is not valid syntax

[danthedaniel]

Should add a check for MySQL/PGSQL and use different query strings

[danthedaniel]

Made a new PR:

#804