Added new command to show all available installable versions

[Garfield-fr]

Example of output:

Available tags version
+--------+-----------+
| Type   | Version   |
+--------+-----------+
| lts    | 2.8.18    |
| latest | 3.2.4     |
| dev    | 3.3.0-DEV |
+--------+-----------+
Available versions by branch
+----------+-----------------------------------------------------------------+
| Branches | Available versions                                              |
+----------+-----------------------------------------------------------------+
| 2.3      | 2.3.21, 2.3.22, 2.3.23, 2.3.24, 2.3.25, 2.3.26, 2.3.27, 2.3.28, |
|          | 2.3.29, 2.3.30, 2.3.31, 2.3.32, 2.3.33, 2.3.34, 2.3.35, 2.3.36, |
|          | 2.3.37, 2.3.38, 2.3.39, 2.3.40, 2.3.41, 2.3.42                  |
+----------+-----------------------------------------------------------------+
| 2.5      | 2.5.0, 2.5.1, 2.5.2, 2.5.3, 2.5.4, 2.5.5, 2.5.6, 2.5.7,         |
|          | 2.5.8, 2.5.9, 2.5.10, 2.5.11, 2.5.12                            |
+----------+-----------------------------------------------------------------+
| 2.6      | 2.6.0, 2.6.1, 2.6.2, 2.6.3, 2.6.4, 2.6.5, 2.6.6, 2.6.7,         |
|          | 2.6.8, 2.6.9, 2.6.10, 2.6.11, 2.6.12, 2.6.13                    |
+----------+-----------------------------------------------------------------+
| 2.7      | 2.7.0, 2.7.1, 2.7.2, 2.7.3, 2.7.4, 2.7.5, 2.7.6, 2.7.7,         |
|          | 2.7.8, 2.7.9, 2.7.10, 2.7.11, 2.7.12, 2.7.13, 2.7.14, 2.7.15,   |
|          | 2.7.16, 2.7.17, 2.7.18, 2.7.19, 2.7.20, 2.7.21, 2.7.22, 2.7.23, |
|          | 2.7.24, 2.7.25                                                  |
+----------+-----------------------------------------------------------------+
| 2.8      | 2.8.0, 2.8.1, 2.8.2, 2.8.3, 2.8.4, 2.8.5, 2.8.6, 2.8.7,         |
|          | 2.8.8, 2.8.9, 2.8.10, 2.8.11, 2.8.12, 2.8.13, 2.8.14, 2.8.15,   |
|          | 2.8.16, 2.8.17, 2.8.18                                          |
+----------+-----------------------------------------------------------------+
| 3.0      | 3.0.0, 3.0.1, 3.0.2, 3.0.3, 3.0.4, 3.0.5, 3.0.6, 3.0.7,         |
|          | 3.0.8, 3.0.9                                                    |
+----------+-----------------------------------------------------------------+
| 3.1      | 3.1.0, 3.1.1, 3.1.2, 3.1.3, 3.1.4, 3.1.5, 3.1.6, 3.1.7,         |
|          | 3.1.8, 3.1.9, 3.1.10                                            |
+----------+-----------------------------------------------------------------+
| 3.2      | 3.2.0, 3.2.1, 3.2.2, 3.2.3, 3.2.4                               |
+----------+-----------------------------------------------------------------+

[Pierstoval]

I'm not sure this is very useful, as we already have http://symfony.com/roadmap 😕

I just answer this because of #82/#84 , actually 😄

[stof]

I'm also not sure about that. It does not make sense to select an older version that the latest one for each branch anyway.

[javiereguiluz]

Let's close this old PR because the Symfony Installer is no longer adding new features now that Symfony Flex has made it obsolete. @Garfield-fr thanks for your contribution anyway!