Replaced foreign keys with simple indexes

[FrittenKeeZ]

Also added index to entries order, and re-aligned migrations with Laravel's stub.

Fixes #97

[what-the-diff[bot]]

• The origin_id column is now indexed.
• The order column is now indexed.
• In the create_entries_table migration, foreign key constraints are removed from the origin id and form id columns respectively (lines 14-19 & lines 24-29). This means that these two tables will no longer be linked by a foreign key constraint in production environments where this code has been deployed to; however, they still remain linked via an index on each table's respective origin or form field which can help with performance when querying for data across both tables but does not enforce referential integrity between them as would have previously been done through a foreign key constraint before it was removed here in this commit/diff above..

[jasonvarga]

Sorry I deleted my comment because right after I realized how long this has been opened, I didn't want to bother you. I was going to just sort it out myself. 😊 But thanks for updating that.

[ryanmitchell]

@jasonvarga I know you've got a seperate fix for the FK errors at https://github.com/statamic/eloquent-driver/pull/160 but I still think this is worth merging as it solves Jack's original issue. Do you have any concerns?

[ryanmitchell]

@FrittenKeeZ I've added an update script to provide migrations for existing installs so that the table definitions match going forward.