Adding Swap to Vaprobash

- See #338
- Adds optional Swap to the Vagrant box using a new variable called `server_swap`. Set it to `false` if you don't want any Swap.
- Will fix #336
Merge pull request #342 from Ilyes512/add-swap

Adding Swap to Vaprobash
Merge branch 'develop'
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Some minor "improvements"

Based on laravel/settler:
- Added redis_persistent variable.
- Using PPA:rwky/redis for latest stable redis.
- Added php5-redis.
- Added some more PHP config (memory_limt is set to 256MB instead of 128MB, cgi.fix_pathinfo is disabled, ...).
- Cleaned up "Enable remote acces" in mysql.sh and maria.db.
- The variable booleans check are case-insensitive and space-insensitive (ie "true", "True ", "TRUE" are all recognized as true).

Misc improvements:
- Updated default global composer package version using Tilde Operator.
- Add --prefer-dist to composer update