Support `lenient` setting with `LocalDateDeserializer`

[cowtowncoder]

(note: follow-up on #106)

It seems like integer values are allowed for LocalDate: this meaning number of days since 1970-01-01 UTC. While this is useful for some users, others may want to prevent that -- this can be supported by using leniency setting (@JsonFormat and/or type/global configOverrides).

Will also benefit from eventual implementation of

FasterXML/jackson-databind#2424

which hopefully makes it in 2.10: it will add a way to define global "strict as baseline" configuration.

[cowtowncoder]

/cc @esHack

Use of leniency property now added for 2.10, deserializer for LocalDate.
Currently it needs to be enabled either on property (add @JsonFormat(lenient = OptBoolean.FALSE)), or via config overrides for all instances of LocalDate:

    ObjectMapper mapper = ...
    mapper.configOverride(LocalDate.class)
            .setFormat(JsonFormat.Value.forLeniency(false));

and this will prevent acceptance of number for LocalDate values.

I will also work on databind issue referenced above to make it easy to declare globally that "strict" mode should be used (unless overridden for specific type or property), which could be even better for many users.