refactor blockeq requests to use OkHttp

[dabitdev]

This two request should use OkHttp instead of Volley and they should share the okHttClient instance with Horizon.
"https://api.blockeq.com/directory/assets"
"https://api.blockeq.com/directory/exchanges?asArray"

[Daniel-Wang]

Addressed in part in PR #132

[dabitdev]

Stellar sdk 0.3.3

1 - to use stellar sdk 0.3.3 retrofit has to be 2.4.0 because it was clashing with okhttp version 3.12 vs 3.11 (in library)
2 - Issue in Retrofit.Builder().baseUrl("url")), does not exist the method it requires to create base url like val httpUrl = HttpUrl.parse("https://api.blockeq.com/")
3 - Clash in publicsuffixes.gz'
Solution

packagingOptions {
        /* this is to avoid the clash between the shadowed okhttp form stellar sdk */
        exclude 'okhttp3/internal/publicsuffix/publicsuffixes.gz'
    }

4 - Clash with okhttp3 classes, solution exclude dependencies

 implementation("com.squareup.retrofit2:retrofit:$retrofit") {
        exclude group: 'com.squareup.okhttp3', module: 'okhttp'
    }

    implementation("com.squareup.retrofit2:converter-gson:$retrofit") {
        exclude group: 'com.squareup.retrofit2', module: 'retrofit'
        exclude group: 'com.google.code.gson', module: 'gson'
    }

4.1 - make sure to use retrofit = '2.4.0' to match okhttp version methods.
5 - [NOT SOLVED] gson from the library is version 2.4.0 and the com.squareup.retrofit2:converter-gson:2.4.0 is using 2.8.2. The old version does not have the method Gson$newJsonReader

java.lang.NoSuchMethodError: No virtual method newJsonReader(Ljava/io/Reader;)Lcom/google/gson/stream/JsonReader; in class Lcom/google/gson/Gson; or its super classes (declaration of 'com.google.gson.Gson' appears in /data/app/com.blockeq.stellarwallet-StDjOngbQTC8c-vHPahKLA==/split_lib_dependencies_apk.apk)

Stellar sdk 0.4.1

Everything gets shadowed under shadow.* package

[dabitdev]

done in latest version 2.0.7.5