(cherry picked from commit cf9be85)
(cherry picked from commit d56ef58)

(cherry picked from commit 295a046)
(cherry picked from commit 5cc964c)

(cherry picked from commit e2e6a79)
(cherry picked from commit 616bf13)

(cherry picked from commit 56ae287)
(cherry picked from commit b4c40de)

* Safer Velocity configuration
* New "message.templates.allowed-config" config
* Remove "UnmodifiableConfiguration" in favour of a
  simple Map of whitelisted Config keys/values
* Centralise Velocity config in core Utils
* Small javadoc changes

(cherry picked from commit b2d6141)
(cherry picked from commit 9b4e48f)

(cherry picked from commit 6b66531)
(cherry picked from commit 400d95b)

(cherry picked from commit 5803819)
(cherry picked from commit f63a615)

(cherry picked from commit c70dc74)
(cherry picked from commit e7704d7)

(cherry picked from commit 65092e1)

Includes some central validation that other classes
can make use of.
However, it may be overly restrictive.
And we may need to allow multiple separate absolute base paths for each config?

(cherry picked from commit dddabe6)
(cherry picked from commit c2c4088)

# Conflicts:
#	dspace-api/src/main/java/org/dspace/core/LDN.java

(cherry picked from commit 8e3c640)
(cherry picked from commit aee73a3)

(cherry picked from commit 83bbb35)

# Conflicts:
#	dspace-api/src/main/java/org/dspace/core/LDN.java
(cherry picked from commit a734a55)

(cherry picked from commit 8084c92)
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(cherry picked from commit 572f952)
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(cherry picked from commit e9cca8e)
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(cherry picked from commit f97b34b)
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(cherry picked from commit 00e4979)
(cherry picked from commit b0130d0)

(cherry picked from commit 6437472)
(cherry picked from commit db7337c)