[Epic] Degree-dependent evolution operators

[ChrizZz110]

Epic for several degree-dependent evolution operators

This epic is used to implement several degree-dependent temporal metrics as operators.
Each operator is a GraphToValue operator. The input is thus a temporal graph as well as the time dimension to consider and the degree type (in/out/both).

• Min/Max/Avg degree evolution (Add Min/Max/Avg graph degree aggregation (static and temporal) #1559)

• Vertex-centric min/max/avg degree evolution (Vertex-centric min/max/avg degree evolution operator #1569)

• Degree range evolution (Degree range evolution operator #1570)

• Degree variance evolution (Degree variance evolution operator #1571)

• Average Nearest Neighbor degree evolution (Average Nearest Neighbor degree evolution operator #1572)

• The operators should be added to package org.gradoop.temporal.model.impl.operators.metric.

• Each operator should be a class with naming XXXEvolution, e.g., DegreeRangeEvolution or VertexCentricMinDegreeEvolution.

• Each operator must implement the Interface UnaryBaseGraphToValueOperator<TemporalGraph, DataSet<YYY> with YYY as the output data type, e.g., Tuple3<Long, Long, Integer> for defining a time interval and its corresponding degree value.

• Each operator should be able to configure degree type and time dimension.

• All new map, flatmap, join functions should be placed as classes in package org.gradoop.temporal.model.impl.operators.metric.functions

Instructions for DigDataPraktikum

1. Log in to github with your own account
2. fork gradoop into your own repositories by clicking the fork button
3. clone the forked gradoop repo to your local machine
4. use IntelliJ as IDE
5. check out the develop branch of your forked repo (if it is not already done) and update the latest changes with git pull
6. Create a new local branch with the naming convention #issueNr_short_name e.g., #1569_vertex_centric_degree
7. Work in this branch to solve the issue. Don't forget unit tests.
8. Commit your changes with a commit message that always starts with [#issueNr] description that the commit can be assigned to the issue
9. Run locally mvn clean verify -DskipTests to verify the checkstyle
10. Run locally mvn clean install to run all tests (time consuming)
11. If everything is fine, push your changes to your forked gradoop repo and open a PullRequest to branch develop of the origin gradoop repo.