New buckets for 0.6.0: small changes

- Fix bucket delete

- fix merge of bucket creation date

- Replace deletable with option in aliases
    Rationale: if two aliases point to conflicting bucket, resolving
    by making an arbitrary choice risks making data accessible when it
    shouldn't be. We'd rather resolve to deleting the alias until
    someone puts it back.

src/util/crdt/crdt.rs

@@ -1,5 +1,3 @@
-use crate::data::*;
-
 /// Definition of a CRDT - all CRDT Rust types implement this.
 ///
 /// A CRDT is defined as a merge operator that respects a certain set of axioms.
@@ -87,7 +85,3 @@ impl AutoCrdt for String {
 impl AutoCrdt for bool {
 	const WARN_IF_DIFFERENT: bool = true;
 }
-
-impl AutoCrdt for FixedBytes32 {
-	const WARN_IF_DIFFERENT: bool = true;
-}