Add titan-solr to titan-all

Since titan-dist (which builds the zipfiles) relies on titan-all, this
also adds titan-solr to the zipfiles.
Manage the spatial4j version in top-level pom

Spatial4j is declared as a dependency in titan-core and in titan-solr.
The version is now controlled from the top-level titan pom.  This was
necessary when compiling with an older, pre 4.8.1 Solr version that
had a different Spatial4j dependency version.
Fix bogus copy-pasted section header in solr docs
Expand the manual Solr field def paragraph a bit
Add sample config for Cassandra + Solr
Flesh out Solr dynamic fields docs a bit
Add Solr troubleshooting entry on JTS jar

Solr can throw an exception during core creation when the jts jar is
absent from the Solr daemon classpath and schema.xml defines geo
fields.  This is a consequence of Spatial4j declaring JTS as an
optional dependency.

This commit adds a troubleshooting entry to the Solr docs that
summarizes the resulting exceptions and describes determination of the
appropriate JTS version to install.
Add a Solr doc section specific to DSE

This commit fills the formerly-empty DSE Search section under the Solr
doc chapter.  The steps were tested on DSE 4.5.2 and a 0.5.1-SNAPSHOT
version shortly before 0.5.1 went final.
Add Solr chapter to docs TOC
Make doc xref links same color as external links

There was no real reason for xref links (internal to the
documentation) to be different color from links to external resources.
The xref color was also a very dark grey bordering on black, making
them barely stand out as links.  Now xref links are the same bright
red as external links.