Add VariableManager, RpcClient classes, and cache enhancements

src/Socialbox/Classes/Resources/database/variables.sql

@@ -0,0 +1,11 @@
+create table variables
+(
+    name        varchar(255)                           not null comment 'The name of the variable'
+        primary key comment 'The unique index for the variable name',
+    value       text                                   null comment 'The value of the variable',
+    `read_only` tinyint(1) default 0                   not null comment 'Boolean indicator if the variable is read only',
+    created     timestamp  default current_timestamp() not null comment 'The Timestamp for when this record was created',
+    updated     timestamp                              null comment 'The Timestamp for when this record was last updated',
+    constraint variables_name_uindex
+        unique (name) comment 'The unique index for the variable name'
+);