Avoid ValueAfterTable when serializing configs

[drdrsh]

It seems that the toml serializer maintains the order of fields in the struct in the final file. So we should always put simple fields before nested fields in all serializable structs to avoid ValueAfterTable errors.
These errors occur when the toml serializer is about to produce ambiguous toml structure like the one below

[main]
field1_under_main = 1
field2_under_main = 2

[main.subconf]
field1_under_subconf = 1
field3_under_main = 3 # This field will be interpreted as being under subconf and not under main