Updated custom Eloquent relations for Laravel 5.8

[lcharette]

• Updated custom Eloquent relations for Laravel 5.8
• Removed belongsToManyConstrained (deprecated in 4.1.6)

Related to Issue #907

[codecov]

Codecov Report

Merging #996 into develop will increase coverage by 0.27%.
The diff coverage is 87.27%.

@@              Coverage Diff              @@
##             develop     #996      +/-   ##
=============================================
+ Coverage      66.83%   67.11%   +0.27%     
+ Complexity      2082     2073       -9     
=============================================
  Files            160      159       -1     
  Lines           6793     6753      -40     
=============================================
- Hits            4540     4532       -8     
+ Misses          2253     2221      -32

Impacted Files	Coverage Δ	Complexity Δ
...t/src/Database/Migrations/v400/ActivitiesTable.php	100% <ø> (ø)	4 <0> (ø)	⬇️
...ccount/src/Database/Migrations/v400/RolesTable.php	100% <ø> (ø)	4 <0> (ø)	⬇️
...count/src/Database/Migrations/v400/GroupsTable.php	100% <ø> (ø)	4 <0> (ø)	⬇️
...nt/src/Database/Migrations/v400/RoleUsersTable.php	100% <ø> (ø)	4 <0> (ø)	⬇️
.../Database/Migrations/v400/PermissionRolesTable.php	100% <ø> (ø)	4 <0> (ø)	⬇️
...src/Database/Migrations/v400/PersistencesTable.php	100% <ø> (ø)	4 <0> (ø)	⬇️
...c/Database/Migrations/v400/PasswordResetsTable.php	100% <ø> (ø)	4 <0> (ø)	⬇️
...ore/src/Database/Migrations/v400/SessionsTable.php	100% <ø> (ø)	4 <0> (ø)	⬇️
.../src/Database/Migrations/v400/PermissionsTable.php	100% <ø> (ø)	5 <0> (ø)	⬇️
app/sprinkles/core/src/Csrf/SlimCsrfProvider.php	81.48% <ø> (ø)	12 <0> (ø)	⬇️
... and 12 more

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