Fixed invalid url in watchdog messages and converted deprecated watchdog...

Love the module... I want to see it succeed....

After creating a new flag I went to 

/admin/reports/dblog

to look at the associated message, with its  handy 'Edit' link.
the  link is unfortunately invalid :(

"If" you created a flag called "test" the the link url would be 

/admin/structure/flags/manage/test/edit 

in the current way of doing things the problem is the appended '/edit' in mucks the link up.

I have test it and shown the 

/admin/structure/flags/manage/test/ works just fine.

Also watchdog is deprecated, but $this->logger comes for 'free' from FormBase.